Understanding stack operations is crucial for developing efficient and robust microcontroller applications. The 8051 microcontroller, a popular choice for embedded systems, offers a powerful stack mechanism that plays a vital role in managing program flow and data storage. In this comprehensive guide, we’ll delve deep into the intricacies of 8051 stack operations, exploring how to push your programming skills to the limit and maximize the potential of this versatile microcontroller.

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The 8051 microcontroller utilizes a stack to temporarily store data and manage subroutine calls. This stack is a Last-In-First-Out (LIFO) data structure, meaning that the last item pushed onto the stack is the first one to be retrieved. Let’s examine the key aspects of the 8051 stack:

The Stack Pointer (SP) is an 8-bit register that keeps track of the top of the stack. When the 8051 is reset, the SP is initialized to 07H, indicating that the stack begins at memory location 08H. As we push data onto the stack, the SP is automatically incremented, and when we pop data off the stack, it’s decremented.

Two primary operations are performed on the stack:

1. PUSH: This operation adds data to the top of the stack.
2. POP: This operation retrieves data from the top of the stack.

Let’s explore these operations in more detail.

The PUSH operation is fundamental to stack management in the 8051. When we push data onto the stack, several steps occur:

1. The Stack Pointer (SP) is incremented.
2. The data is stored at the memory location pointed to by the SP.

Here’s an example of how to push the contents of the accumulator onto the stack:

MOV A, #42H  ; Load the accumulator with the value 42H
PUSH ACC     ; Push the accumulator contents onto the stack

In this code snippet, we first load the accumulator with the hexadecimal value 42H. The PUSH instruction then increments the SP and stores the accumulator’s contents at the new stack top.

The POP operation is the counterpart to PUSH, allowing us to retrieve data from the stack. When we pop data, the following steps take place:

1. The data at the current stack top is read.
2. The Stack Pointer (SP) is decremented.

Here’s how we can pop data from the stack into the accumulator:

POP ACC      ; Pop the top stack value into the accumulator

This instruction retrieves the value from the top of the stack, stores it in the accumulator, and then decrements the SP.

Now that we’ve covered the basics, let’s explore some advanced techniques to push your 8051 stack operations to the limit.

One of the most powerful applications of the stack is in managing nested subroutine calls. When a subroutine is called, the program counter (PC) is automatically pushed onto the stack, allowing the program to return to the correct location after the subroutine completes.

Consider this example of nested subroutine calls:

MAIN:
    ACALL SUB1
    ; More code here
    SJMP $

SUB1:
    ; Subroutine 1 code
    ACALL SUB2
    RET

SUB2:
    ; Subroutine 2 code
    RET

In this code, SUB1 calls SUB2, demonstrating how the stack manages multiple levels of subroutine calls.

Another crucial use of the stack is preserving register contents across subroutine calls. This technique is essential for maintaining data integrity in complex programs.

SUBROUTINE:
    PUSH ACC     ; Save accumulator
    PUSH PSW     ; Save Program Status Word

    ; Subroutine code here

    POP PSW      ; Restore Program Status Word
    POP ACC      ; Restore accumulator
    RET

By pushing important registers onto the stack at the beginning of a subroutine and popping them off at the end, we ensure that the calling routine’s register values are preserved.

To push your 8051 programming to the limit, it’s crucial to optimize stack usage. Here are some advanced techniques:

Strive to minimize the stack depth by carefully managing subroutine calls and local variables. This approach helps prevent stack overflow and conserves valuable RAM.

The 8051 offers multiple register banks. By utilizing these effectively, you can reduce the need for stack operations:

    MOV PSW, #00H  ; Select Register Bank 0
    ; Use R0-R7 from Bank 0

    MOV PSW, #08H  ; Select Register Bank 1
    ; Use R0-R7 from Bank 1

For very short subroutines, consider using inline code instead of subroutine calls to reduce stack usage:

; Instead of:
; ACALL SHORT_SUBROUTINE

; Use inline code:
    INC R0
    MOV A, @R0
    ADD A, #05H

The 8051 provides interrupts that can be crucial for managing stack operations:

While the 8051 doesn’t have a built-in stack overflow interrupt, we can implement our own detection mechanism:

    MOV SP, #7FH      ; Set stack pointer to top of RAM
    MOV 7FH, #0AAH    ; Place marker at top of stack

CHECK_OVERFLOW:
    MOV A, 7FH
    CJNE A, #0AAH, OVERFLOW_HANDLER
    ; Continue with normal operation

OVERFLOW_HANDLER:
    ; Handle stack overflow

This code sets a marker at the top of the stack and regularly checks if it has been overwritten, indicating a stack overflow.

Let’s explore some real-world applications that showcase the power of mastering 8051 stack operations:

Recursive algorithms heavily rely on stack operations. Here’s a simple example of a recursive factorial calculation:

FACTORIAL:
    ; Input in R7, result in R1:R0
    MOV A, R7
    JZ FACT_DONE    ; If input is 0, return 1
    DEC A
    JZ FACT_DONE    ; If input is 1, return 1

    PUSH 07H        ; Save current n
    DEC R7          ; Calculate (n-1)!
    ACALL FACTORIAL
    POP 07H         ; Restore n

    ; Multiply result by n
    MOV A, R7
    MOV B, R0
    MUL AB
    MOV R0, A
    MOV A, R7
    MOV B, R1
    MUL AB
    ADD A, B
    MOV R1, A

    RET

FACT_DONE:
    MOV R1, #00H
    MOV R0, #01H
    RET

This recursive implementation demonstrates how the stack manages local variables and return addresses in a complex algorithm.

A simple task scheduler can be implemented using stack operations:

SCHEDULER:
    PUSH DPL
    PUSH DPH

    ; Task selection logic here
    ; ...

    ; Jump to selected task
    PUSH ACC     ; Save selected task address
    RET          ; 'Return' to the task

TASK_RETURN:
    POP DPH
    POP DPL
    SJMP SCHEDULER

This scheduler uses the stack to manage task switching, demonstrating how stack operations can be used in real-time systems.

Mastering 8051 stack operations is essential for pushing your microcontroller programming skills to the limit. By understanding the intricacies of PUSH and POP operations, optimizing stack usage, and applying advanced techniques, you can develop more efficient and robust embedded systems.

Remember, the key to success lies in practice and experimentation. Try implementing the examples and techniques discussed in this article, and don’t be afraid to push the boundaries of what’s possible with the 8051’s stack capabilities.

As you continue to explore and innovate, you’ll find that the 8051’s stack operations offer a powerful toolset for solving complex programming challenges. By pushing these operations to their limits, you’ll unlock new possibilities in your microcontroller projects and elevate your skills to new heights.

This comprehensive guide explores the intricacies of 8051 external interrupts, providing in-depth knowledge on harnessing external events to enhance microcontroller functionality. We’ll delve into interrupt types, configuration methods, real-world applications, and advanced techniques. By the end of this article, you’ll have a thorough understanding of how to effectively implement external interrupts in your 8051 projects.

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In the realm of microcontroller programming, interrupts play a crucial role in creating responsive and efficient systems. The 8051 microcontroller family, with its rich history and continued relevance in embedded systems, offers powerful interrupt capabilities that allow developers to harness the power of the outside world. In this article, we’ll explore the fascinating world of 8051 external interrupts, uncovering their potential to revolutionize your projects.

External interrupts are hardware-triggered events that cause the microcontroller to temporarily pause its current execution and respond to an external stimulus. The 8051 microcontroller provides two dedicated external interrupt pins: INT0 (P3.2) and INT1 (P3.3). These interrupts can be configured to respond to either falling edge or low-level triggers, offering flexibility in interrupt handling.

1. Two independent external interrupt sources (INT0 and INT1)
2. Configurable trigger modes (falling edge or low-level)
3. Individual enable/disable control
4. Programmable priority levels
5. Interrupt vector addresses for quick response

To harness the power of external interrupts, we need to configure them properly. Let’s explore the step-by-step process of setting up an external interrupt on the 8051:

1. Enable global interrupts: Set the EA (Enable All) bit in the IE (Interrupt Enable) register.
2. Enable specific external interrupt: Set the EX0 (External Interrupt 0) or EX1 (External Interrupt 1) bit in the IE register.
3. Configure interrupt trigger mode: Use the IT0 and IT1 bits in the TCON (Timer Control) register to select edge or level triggering.
4. Set interrupt priority (optional): Configure the IP (Interrupt Priority) register if needed.
5. Implement the Interrupt Service Routine (ISR): Write the code to handle the interrupt event.

Here’s a code snippet demonstrating the configuration of External Interrupt 0:

#include 

void ext_int0_isr(void) __interrupt(0) {
    // Interrupt Service Routine code here
}

void main() {
    EA = 1;  // Enable global interrupts
    EX0 = 1; // Enable External Interrupt 0
    IT0 = 1; // Set INT0 to trigger on falling edge

    while(1) {
        // Main program loop
    }
}

External interrupts open up a world of possibilities for creating responsive and efficient embedded systems. Let’s explore some practical applications:

One common use of external interrupts is to handle button presses while avoiding the effects of button bounce. Here’s a simple circuit diagram and code snippet:

   VCC
    |
    |
   [R]
    |
    |------|
    |      |
   [SW]    |
    |      |
   GND    P3.2 (INT0)

#include 

volatile bit button_pressed = 0;

void ext_int0_isr(void) __interrupt(0) {
    button_pressed = 1;
    // Disable interrupt to avoid multiple triggers
    EX0 = 0;
}

void main() {
    EA = 1;  // Enable global interrupts
    EX0 = 1; // Enable External Interrupt 0
    IT0 = 1; // Set INT0 to trigger on falling edge

    while(1) {
        if (button_pressed) {
            // Handle button press
            button_pressed = 0;
            // Re-enable interrupt after debounce delay
            __delay_ms(50);
            EX0 = 1;
        }
    }
}

External interrupts are ideal for interfacing with rotary encoders, allowing precise position tracking. Here’s a basic circuit and code example:

   VCC
    |
   [R]     [R]
    |       |
    |-------|
    |       |
   [A]     [B]
    |       |
   P3.2    P3.3
  (INT0)  (INT1)
    |       |
   GND     GND

#include 

volatile int encoder_position = 0;

void ext_int0_isr(void) __interrupt(0) {
    if (P3_3) {
        encoder_position++;
    } else {
        encoder_position--;
    }
}

void main() {
    EA = 1;  // Enable global interrupts
    EX0 = 1; // Enable External Interrupt 0
    IT0 = 1; // Set INT0 to trigger on falling edge

    while(1) {
        // Use encoder_position as needed
    }
}

The 8051 supports nested interrupts, allowing higher-priority interrupts to interrupt lower-priority ones. To implement nested interrupts:

1. Configure interrupt priorities using the IP register.
2. Enable nested interrupts by setting the EA bit within ISRs.

#include 

void high_priority_isr(void) __interrupt(0) {
    EA = 1;  // Enable nested interrupts
    // High-priority interrupt handling
}

void low_priority_isr(void) __interrupt(2) {
    // Low-priority interrupt handling
}

void main() {
    EA = 1;   // Enable global interrupts
    EX0 = 1;  // Enable External Interrupt 0
    EX1 = 1;  // Enable External Interrupt 1
    IT0 = 1;  // Set INT0 to trigger on falling edge
    IT1 = 1;  // Set INT1 to trigger on falling edge
    PX0 = 1;  // Set INT0 to high priority

    while(1) {
        // Main program loop
    }
}

External interrupts can be used to implement efficient state machines for complex system control. Here’s an example of a simple traffic light controller:

#include 

enum TrafficLightState {
    RED,
    GREEN,
    YELLOW
};

volatile enum TrafficLightState current_state = RED;

void ext_int0_isr(void) __interrupt(0) {
    switch (current_state) {
        case RED:
            current_state = GREEN;
            break;
        case GREEN:
            current_state = YELLOW;
            break;
        case YELLOW:
            current_state = RED;
            break;
    }
}

void main() {
    EA = 1;  // Enable global interrupts
    EX0 = 1; // Enable External Interrupt 0
    IT0 = 1; // Set INT0 to trigger on falling edge

    while(1) {
        switch (current_state) {
            case RED:
                P1 = 0x01; // Red LED on
                break;
            case GREEN:
                P1 = 0x02; // Green LED on
                break;
            case YELLOW:
                P1 = 0x04; // Yellow LED on
                break;
        }
    }
}

To make the most of 8051 external interrupts, consider these best practices:

1. Keep ISRs short and efficient: Minimize the time spent in interrupt routines to ensure responsiveness.
2. Use volatile variables for shared data between ISRs and the main program.
3. Implement proper debouncing for switch inputs to avoid false triggers.
4. Consider using edge-triggered interrupts for most applications to avoid missed events.
5. Utilize interrupt priorities to handle time-critical events effectively.

8051 external interrupts offer a powerful means of interfacing with the outside world, enabling responsive and efficient embedded systems. By mastering the configuration, implementation, and advanced techniques discussed in this article, you’ll be well-equipped to harness the full potential of external interrupts in your 8051 projects.

From simple button debouncing to complex state machines, the applications of external interrupts are limited only by your imagination. As you continue to explore and experiment with these capabilities, you’ll discover new ways to push the boundaries of what’s possible with the venerable 8051 microcontroller family.

Remember, the key to success lies in understanding the underlying principles, careful planning, and meticulous implementation. With practice and creativity, you’ll soon be crafting sophisticated interrupt-driven systems that seamlessly interact with the world around them.

Diagnostics functionality is very crucial for repairing and maintaining any system. The complex system often need to identify and communicate faults to different subsystems, need calibration functionality, need the ability to read and write specific memory, need security functions. All such features are defined by J1939-73 standard for off-road and heavy vehicles.

The standard defines a diagnostic connector to be used for service tools and defines messages required to perform diagnostic services. Diagnostic messages (DM) are used when a vehicle is repaired as well as during vehicle operation. It allows the exchange of diagnostic information between networked ECUs. This helps to build an intelligent system that can self adjust in presence of faults or compensate as appropriate based on diagnostic information.

This article gives brief information of diagnostics connector and fault handling supported in SAE J1939.

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The off-board diagnostics connector specifications are defined in SAE J1939-13. This standard talks about more details of the connector mounting, serviceability, performance, environmental, physical requirements, and connector mechanical requirements. All these topics are out of the scope of this article, please refer to the standard document for these details.

J1939 CAN diagnostics connector supports twisted shielded pair as well as twisted unshielded wiring. 9-pin CAN diagnostics connector pin designations are shown below.

SAE J1939 diagnostics 9 pin connector

• Pin A – Battery (-)
• Pin B – Battery (+)
• Pin C – CAN_H
• Pin D – CAN_L
• Pin E – CAN_SHLD
• Pin F – SAE J1708 (+)
• Pin G – SAE J1708 (-)
• Pin H – Proprietary OEM Use or Implement Bus CAN_H
• Pin J – Proprietary OEM Use or Implement Bus CAN_L

DTCs are used to report potential fault conditions in the system. A DTC contains four independent fields which give information about the fault being reported by DTC. These fields are,

1. Suspect Parameter Number (SPN)
2. Failure mode identifier (FMI)
3. Occurance Count (OC)
4. SPN Conversion Method (CM)

SPN is a 19-bit number assigned for a specific component or electric subsystem which aids to find the location of a fault. PGNs already defined by application layer documents are used as SPN in diagnostics, so there is no need to define SPNs again. FMI is a 5-bit number that defines the nature of the fault. FMI can indicate a problem with the electrical systems or abnormal conditions detected. Below is the list of FMIs defined in the standard.

Failure Mode Indicators

OC is a 7-bit number and it tells how many times failure has occurred. Every time fault goes from inactive to active, the OC is incremented by 1. if fault becomes active for more than 126 times the OC remains 126.

CM is 1 bit to indicate the DTC conversion method. This bit defines byte alignment in the DTC.

The standard defines multiple Diagnostic Messages (DM) to accomplish a specific purpose.  DM1 message transmit active DTCs while DM2 message transmits non-active/ previously active DTCs. DM1 and DM2 messages may contain multiple DTCs. In the case of more than one DTC, DM1 and DM2 messages are transmitted using Transport protocol (TP).

DM1 and DM2 messages contain 4 bytes of data per trouble code. The alignment of these 4 bytes defined by CM bit. Older SAE J1939 specifications supported 3 methods for SPN while the newer versions of specifications support only one conversion method called method 4. If CM bit is set to 1 that means DTC bytes are aligned using a newer conversion method. If CM is 0 (zero) means one of the three DTC conversion methods is used and ECU manufacture shall know which of the three methods is used.

Method 4 is recommended method.

J1939 DTC Conversion Methods

In next section we can see DTC related diagnostic messages supported in J1939.

DM1 message contains information of all active DTCs and diagnostic lamp status. The lamp status supports visual diagnostics and used by fault indicators on a vehicle dashboard. SAE J1939 diagnostic supports four types of lamp status. Malfunction Indicator Lamp (MIL) shows malfunctions related to emission. Red Stop Lamp (RSL) indicates serious faults that require the vehicle to stop. Amber Warning Lamp (AWL) signals less critical faults and vehicles need not be immediately stopped. The vehicle can still run while these faults are active. Protection Lamp (PL) indicates faults that are not because of electronics like hydraulic fluid temperature is rising beyond prescribed temperature range. All these lamp status supports 4 states; Lamp OFF, Lamp Steady ON, Lamp Flashing 1 Hz, Lamp flashing 2 Hz.  if ECU does not have an active fault, them lamp status shall be set to Lamp Off.

DM1 message uses PGN 65226 (0xFECA). DM1 message is sent periodically only when there is an active DTC or in the response of the request. If there is more than 1 active DTC, this message is sent using the transport protocol. The transmission rate of this message is 1 second. When a DTC becomes active DM1 message is sent immediately and then every one second thereafter. If a different DTC changes state (inactive to active or active to inactive) within the 1 second update period, a DM1 message is transmitted to communicate the change. To avoid high transmission rates, it is recommended that only one state change of one DTC shall be transmitted in one second. For a DTC becoming active and inactive twice within the 1-second interval, only one DM1 message is sent in the one-second interval. The following table shows the DM1 message format.

DM2 messages contain a list of previously active DTCs. This message contains all the DTCs which were previously active and the occurrence count is non zero. Like DM1 message if the number of DTCs is more than 1, DM2 message is sent using the transport protocol. This message is not a periodic message, so it is sent only on request using PGN 59904. If this PGN is not supported then a NACK response shall be sent. DM2 message uses 65227 (0xFECB). The following table shows DM2 message details.

DM3 message is used to clear all diagnostic information related to previously active DTCs. This information may include the following items.

• Number of previously active DTCs
• Previously active DTCs
• Freeze frame data
• Status of system monitoring tests
• On-Board monitoring tests
• Distance traveled while MIL (malfunction indicator lamp) is active
• Performance monitoring information
• manufacturer specific diagnostic data

DM3 message is sent using request PGN 59904. Once the previously active diagnostic data is clear or there is no previously active DTC data, the positive acknowledgment is sent by the controller. If the diagnostic data clear operation is failed or the controller could not perform the operation for some reason, then a negative acknowledgment is sent by the controller.

DM3 message does not affect active DTC data. The below table shows DM3 message details.

DM4 message (PGN 65229) is used to read freeze frame data. The freeze-frame contains recorded data corresponding to a DTC when the fault has occurred. A freeze-frame is associated with only DTC and a DTC can have only one freeze-frame. The maximum number of bytes in a freeze frame data can be 1785 bytes so that it can fit into the TP frame. DM4 message is not a periodic message and requested using PGN 59904. The controller shall send NACK if the DM4 message is not supported. The below table shows DM4 message details.

DM11 messages used PGN 65235 (0xFED3), This message is used to clear diagnostic data for active DTCs. Working on this message is exactly the same as the DM3 message.

Below table shows DM11 message details.

DM12 messages send information of active DTCs only related to emission. This message contains lamp status and a list of DTCs. if there are more than 1 DTC then transport protocol is used to transmit this message. This message is not periodic and sent only when requested using request PGN 59904. The following table shows DM12 message format.

J1939/73 specifications define application-layer diagnostics and calibration. There are a number of predefined diagnostics messages.  Faults can be identified using diagnostic trouble code (DTC) which is a 32-bit identifier. DTC includes 4 components; SPN, FMI, OC, and CM. The DTC together with source address is used to identify the fault in a specific subsystem or component.

With the DM1, DM2, and DM12 messages one can read Active and previously active DTC data from the controller. To clear DTC data DM3 and DM11 messages are used. DM22 message is used to clear selected individual DTC. Freeze frame can be read using DM4 messages.

J1939 Diagnostics Part 2

In the realm of motor control, Pulse Width Modulation (PWM) stands as a cornerstone technique, and when combined with the versatile 8051 microcontroller, it opens up a world of possibilities for precise and efficient motor management. We’ll dive deep into the intricacies of implementing PWM using the 8051, exploring its applications in controlling various types of motors, including SC (Series-Compensated) motors, BLDC (Brushless DC) motors, and stepper motors.

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Pulse Width Modulation is a powerful method for controlling the amount of power delivered to a load, such as a motor, without incurring the losses associated with linear power control. By rapidly switching a signal between on and off states and varying the duty cycle, we can effectively simulate an analog output with a digital signal.

• Duty Cycle: The proportion of ‘on’ time to the total time period
• Frequency: The rate at which the PWM signal completes a cycle
• Resolution: The precision with which we can control the duty cycle

The 8051 microcontroller, with its robust architecture, provides an excellent platform for generating PWM signals. We’ll utilize the timer/counter modules of the 8051 to create precise PWM outputs.

#include  void pwm_init() { TMOD = 0x01; // Timer 0, mode 1 (16-bit) TH0 = 0xFF; // Set initial timer value TL0 = 0x00; ET0 = 1; // Enable Timer 0 interrupt EA = 1; // Enable global interrupts
    TR0 = 1;      // Start Timer 0
}

void pwm_set_duty(unsigned char duty) {
    TH0 = 0xFF - duty;
}

void timer0_isr() __interrupt(1) {
    P1_0 = !P1_0;  // Toggle PWM output pin
    TH0 = 0xFF;    // Reset timer
}

void main() {
    pwm_init();
    while(1) {
        // Main program loop
        pwm_set_duty(128);  // 50% duty cycle
    }
}

This code sets up Timer 0 to generate a PWM signal on pin P1.0. The duty cycle can be adjusted by calling pwm_set_duty() with a value between 0 and 255.

Series-Compensated (SC) motors are known for their high starting torque and ability to operate at variable speeds. Implementing PWM control for SC motors using the 8051 allows for precise speed regulation and improved efficiency.

        +5V
         |
         |
    +----|----+
    |    |    |
    |    R    |
    |    |    |
 +--|----+----|-+
 |  |         | |
 |  +--[BJT]--+ |
 |      |       |
 |      |       |
[8051]  |       |
 |      |       |
 |    [MOTOR]   |
 |      |       |
 +------+-------+
        |
       GND

In this circuit, we use a BJT (Bipolar Junction Transistor) as a switch, controlled by the PWM signal from the 8051. This allows us to efficiently regulate the power supplied to the SC motor.

Brushless DC (BLDC) motors offer high efficiency and reliability. Controlling a BLDC motor with the 8051 requires a more complex setup, typically involving a three-phase inverter circuit.

       +------------------+
       |                  |
    +--+--+           +---+--+
    |     |           |      |
 [8051]   |   +-----+ |  BLDC |
    |     +---| ESC |-+      |
    |     |   +-----+ | MOTOR|
    |     |           |      |
    +-----+           +------+
       |                  |
       +------------------+

Here, we use an Electronic Speed Controller (ESC) as an intermediary between the 8051 and the BLDC motor. The ESC interprets the PWM signals from the 8051 and generates the appropriate three-phase signals for the motor.

Stepper motors are ideal for applications requiring precise positioning. By using PWM, we can implement microstepping, which allows for smoother and more accurate control.

      +5V
       |
    +--+--+
    |     |
 [8051]   |   +----------+
    |     +---| STEPPER  |
    |     |   | DRIVER   |
    |     |   |   +----+ |
    |     +---|   |    | |
    |     |   |   |MOTOR |
    +-----+   |   |    | |
       |      |   +----+ |
       |      +----------+
       |
      GND

In this setup, we use a stepper motor driver IC to interface between the 8051 and the stepper motor. The PWM signals from the 8051 control the step and direction inputs of the driver.

Synchronous rectification is a technique that can significantly improve the efficiency of motor drives, especially in BLDC and stepper motor applications.

void sync_rect_pwm() {
    // Set up Timer 1 for complementary PWM
    TMOD |= 0x20;  // Timer 1, mode 2 (8-bit auto-reload)
    TH1 = 0x00;    // Set PWM frequency
    TL1 = 0x00;

    // Enable interrupts
    ET1 = 1;
    EA = 1;

    // Start Timer 1
    TR1 = 1;
}

void timer1_isr() __interrupt(3) {
    P1_0 = !P1_0;  // Toggle high-side PWM
    P1_1 = P1_0;   // Complementary low-side PWM
}

This code generates complementary PWM signals, which are crucial for implementing synchronous rectification in motor control applications.

To achieve precise motor control, we often need to implement closed-loop systems using feedback from sensors. The 8051’s ADC capabilities can be leveraged for this purpose.

int error, last_error = 0;
int integral = 0;
int derivative;
int output;

void pid_control(int setpoint, int actual) {
    error = setpoint - actual;
    integral += error;
    derivative = error - last_error;

    output = KP * error + KI * integral + KD * derivative;

    // Apply output to PWM duty cycle
    pwm_set_duty((unsigned char)(output >> 2));

    last_error = error;
}

This PID (Proportional-Integral-Derivative) control algorithm can be used to maintain a desired motor speed or position by continuously adjusting the PWM duty cycle based on feedback.

For SC motors, we can implement a soft-start feature to prevent high inrush currents:

void sc_motor_soft_start() {
    unsigned char duty;
    for(duty = 0; duty < 255; duty++) {
        pwm_set_duty(duty);
        delay_ms(10);  // Gradual increase over ~2.5 seconds
    }
}

BLDC motors require precise timing for commutation. We can use the 8051’s timers to generate the appropriate sequence:

const unsigned char commutation_sequence[] = {
    0b101, 0b100, 0b110, 0b010, 0b011, 0b001
};

void bldc_commutate(unsigned char step) {
    P1 = (P1 & 0xF8) | commutation_sequence[step];
}

Implementing microstepping can significantly improve the smoothness of stepper motor operation:

const unsigned char sine_table[32] = {
    128, 153, 177, 199, 218, 234, 246, 254,
    // ... (remaining values omitted for brevity)
};

void microstep(unsigned char step) {
    unsigned char coil_a = sine_table[step & 0x1F];
    unsigned char coil_b = sine_table[(step + 8) & 0x1F];

    pwm_set_duty_a(coil_a);
    pwm_set_duty_b(coil_b);
}

Implementing energy-efficient motor control is crucial for battery-powered applications and reducing overall power consumption.

We can utilize the 8051’s power-saving features to reduce energy consumption during motor idle periods:

void enter_sleep_mode() {
    PCON |= 0x01;  // Set IDL bit to enter Idle mode
    // CPU will wake up on the next interrupt
}

Adjusting the PWM frequency based on the motor’s operating conditions can optimize efficiency:

void adjust_pwm_frequency(unsigned int rpm) {
    if(rpm < 1000) {
        TH0 = 0xFC;  // Set for lower frequency
    } else {
        TH0 = 0xFF;  // Set for higher frequency
    }
}

Mastering Pulse Width Modulation with the 8051 microcontroller opens up a world of possibilities in motor control applications. From basic speed control to advanced techniques like synchronous rectification and closed-loop systems, the combination of PWM and the 8051 provides a powerful toolset for engineers and hobbyists alike.

By understanding the unique characteristics of SC motors, BLDC motors, and stepper motors, and implementing tailored PWM strategies for each, we can achieve optimal performance and efficiency in a wide range of motor control scenarios. The code snippets and circuit diagrams provided serve as a starting point for your own motor control projects, offering insights into the practical implementation of these concepts.

As we continue to push the boundaries of motor control technology, the fundamental principles of PWM and the versatility of the 8051 microcontroller remain invaluable tools in our arsenal. Whether you’re developing cutting-edge industrial automation systems or working on a DIY robotics project, the knowledge and techniques discussed here will undoubtedly prove useful in your endeavors.

Remember, effective motor control is not just about raw power, but about precision, efficiency, and adaptability. By mastering PWM with the 8051, you’re well-equipped to tackle a wide array of motor control challenges, innovate new solutions, and drive the future of electromechanical systems.

Switches are a very important part of the machine interface. Pressing horn in your car or hitting the call button on your cell phone, we talk to various machines through switches. There are varieties of switches we press, rotate or touch daily.

A radio jumps 2 or 3 channels ahead when you press the tuning button only once. A TV does not respond unless you press the remote button very hard.  A counter in the mall door advances several digits when only one person is passed through the door. We all know these are classic problems with bad switch debouncing. Novice embedded designers often face issues in switch debounce design. This article is a small introduction to the switch debouncing techniques.

switch-release-bounce switch-press-bounce

Table of Contents

Interfacing a switch with a microcontroller looks very simple thing, but a lot of things happen behind the scene when a user presses a button. Understanding the behavior of switches helps in designing a good debouncing policy.

When the contacts of a mechanical switch are pressed, they rebound several times with different frequencies and then settle down to a fixed state. The rebound of mechanical contact is known as bounce. We have a variety of switches; pushbuttons, SPDT, DPDT, latch-able buttons, rotary switches, joysticks, etc. Again these switches come in different sizes and different current ratings. Because of such variations in switches, the bounce is also different in each type of switches. People press buttons in different ways. Some people press buttons very quickly, some push it very slowly, some users do it by hand, some use different objects to reach the switches. So designing the debouncing solution could be tricky sometimes.

What type of switch you choose mainly depends on the application needs. Once you know the bounce timing stats of a particular switch, you can easily design a debouncing policy. The first crucial step is to find Maximum bounce time and that can be easily done by observing the voltage levels at the switch contacts using an oscilloscope. Operate switch with different techniques, slow, fast, with soft-touch, with hard touch, release gently, release fast. Try different combinations of these techniques and collect the bounce statistics. With these statistics, you can easily arrive at the Maximum bounce time for your switches. The switch can have different bounce times when it is closed and when it is opened.

There are some proven techniques used to remove the effect of switch bounce in digital applications. You can use hardware or software debouncing methods. Hardware debouncing consists of simple hardware filters, digital debouncing circuits and dedicated ICs. The software debouncing method utilizes different algorithms, some are microcontroller platform dependant using specific interrupts, some use counters and some use simple delays before re-sampling the inputs.

Single throw buttons, tactile pushbuttons, and board mounted plates are the most common types of switches used in small appliances. Using a simple RC filter circuit is a lot cheaper solution than any other hardware debouncing technique. Low pass RC filter removes high-frequency changes in the switch bounce.

When the switch is open the voltage across capacitor ‘C’ rises at a rate determined by values of ‘R1’, ‘R2’ and ‘C’. Bouncing of the switch slows down the charging rate of capacitor ‘C’. In time the capacitor charge and the output of the NOT gate (Schmitt trigger) give logical zero output.

When the switch is closed the capacitor starts discharging via ‘R2’. Till the time the capacitor is discharged to a significant level, NOT gate sees logical one at its input. Once the switch settled in a stable closed position after bouncing the capacitor ‘C’ discharges completely and reach level zero. And the NOT gate gives logical one output.

Consider the discharging cycle of capacitor ‘C’,

Where

V_c= Voltage across capacitor ‘C’ at time t

V₀= initial voltage across the capacitor ‘C’

t = time in seconds

Switch Debouncing using low pass RC filter

To calculate ‘R₂‘, select ‘V_c‘ such that it is greater than the switching voltage of the NOT gate in the above circuit.

So the equation for ‘R₂‘ will become

Now consider the charging cycle of capacitor ‘C’.

Let R = R1 + R2 then

With this equation, ‘R’ comes to be

V_f is the final voltage of the charged capacitor. It could be 5V or 3.3V or any other value based on your digital circuit. To calculate ‘R’, select ‘V_c‘ that the less than the lower switching limit for high going signal for NOT gate.

The values of ‘R1’ and ‘R2’ can be calculated by the above formulas.

If the value of ‘R’ is less than ‘R2’, then use diode parallel to the ‘R2’ as shown in the diagram below so that you can eliminate ‘R2’ from the charging path.

Switch Debouncing using RC Filter and Diode

SR flip flop latch is a very good debouncer for switches with the double throw. It consists of 2 NAND gates connected as shown in the below diagram.

Switch Debouncing using SR flip Flop

When the switch is in moved to position 1, the output of the latch will be one. If the switch is moved to position 2, the output of the latch will be zero. When the switch is moved between contacts, it bounces a little bit on one contact but does not touch the other contact. So the stable bouncing free output is given by the SR latch.

Since the cheaper alternatives available to fix the bouncing problem, specialized switch debouncing ICs are not very popular. Maxim Integrated Products Inc. is the one leading manufacturer of debouncing ICS. They have different variants with single, dual and octal switch debouncers in one package. These debouncing ICs provide inbuilt ESD protection. More information can be found in the application note 287.

Maxim Switch Debouncing IC MA6816

The basic idea in software debouncing is to sample the input at regular intervals and filter out the glitches. The switch debouncing can be implemented in a number of ways. If you are not much concerned about real-time performance just check the switch input state, then wait a bit and recheck again. If the same state is detected then that can be considered as a stable state of the switch. Another way is to use a counter and check for how long the switch is low or high and if it is consistently low or high for a predefined time then it is considered a stable state of the switch. Sometimes EMI can produce false signals on the microcontroller pin inputs. Software debouncing also filters such noise.

Some care must be taken while designing a debouncing policy. Avoid sampling of switch input at a rate synchronous to other events that can create EMI, e.g. motor direction change frequency or 50Hz/60Hz frequency. Do not connect un-debounced switches directly to the interrupt pins of microcontrollers. Some microcontrollers provide special interrupt pins that have an inbuilt RC filter. Such pins can be used as switch interrupts. Refer to this article to find interrupt handling in 8051 microcontrollers.

Hardware debouncing involves some cost of components and also needs some space on the circuit board. So software debouncing is very popular and different algorithms are being used for the debouncing.

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In this comprehensive guide, we’ll delve deep into the world of 8051 bitwise operations, unveiling the secret techniques that will elevate your programming skills to the next level. We’ll explore the fundamental concepts, advanced strategies, and practical applications of bitwise operations in the 8051 microcontroller. By the end of this article, you’ll have the knowledge and tools to manipulate bits like a true master, optimizing your code and unlocking the full potential of the 8051 architecture.

In the realm of microcontroller programming, particularly with the 8051 architecture, bitwise operations are the secret weapon that separates novice programmers from seasoned experts. These operations allow us to manipulate individual bits within data, enabling precise control over hardware, efficient memory usage, and lightning-fast computations.

As we embark on this journey to master 8051 bitwise operations, we’ll uncover the hidden potential that lies within each bit. From basic concepts to advanced techniques, we’ll equip you with the knowledge to write elegant, efficient, and powerful code that harnesses the true capabilities of the 8051 microcontroller.

Before we dive into the intricacies of advanced bitwise manipulation, let’s establish a solid foundation by revisiting the core bitwise operations available in the 8051 architecture:

1. AND (&): Performs a logical AND operation between corresponding bits of two operands.
2. OR (|): Executes a logical OR operation between corresponding bits of two operands.
3. XOR (^): Applies an exclusive OR operation between corresponding bits of two operands.
4. NOT (~): Inverts all bits of a single operand.
5. Left Shift (): Shifts all bits of an operand to the right by a specified number of positions.

These operations form the building blocks of our bitwise manipulation arsenal. By combining and leveraging these fundamental operations, we can achieve remarkable results in our 8051 programs.

Now that we’ve refreshed our understanding of the basic operations, let’s explore some advanced techniques that will set your code apart:

One of the most common tasks in microcontroller programming is setting or clearing specific bits without affecting others. Here’s how we can achieve this with elegance and efficiency:

// Set bit 3 of PORT1 without affecting other bits
PORT1 |= (1  0) {
    y = a;
} else {
    y = b;
}

// Optimized bitwise approach
int mask = -(x > 0);  // Creates a mask of all 1s if x > 0, all 0s otherwise
y = (a & mask) | (b & ~mask);

This technique eliminates the need for branching, potentially leading to faster execution on the 8051 architecture.

Counting the number of set bits in a byte is a common operation in many algorithms. Here’s an optimized bitwise solution:

unsigned char count_set_bits(unsigned char x) {
    x = (x & 0x55) + ((x >> 1) & 0x55);
    x = (x & 0x33) + ((x >> 2) & 0x33);
    x = (x & 0x0F) + ((x >> 4) & 0x0F);
    return x;
}

This algorithm uses a divide-and-conquer approach, leveraging bitwise operations to count bits in parallel, resulting in fewer overall operations compared to a naive loop-based solution.

For modulo operations with powers of 2, we can use bitwise AND as a fast alternative:

unsigned int fast_modulo(unsigned int x, unsigned int divisor) {
    return x & (divisor - 1);
}

// Usage
unsigned int result = fast_modulo(17, 8);  // Equivalent to 17 % 8 = 1

This technique works because for any power of 2, subtracting 1 creates a bitmask that can be used to efficiently compute the modulo.

To demonstrate the practical application of these bitwise techniques, let’s implement a simple state machine for a traffic light controller using the 8051 microcontroller:

#include 

#define RED    0x01
#define YELLOW 0x02
#define GREEN  0x04

sbit RED_LED    = P1^0;
sbit YELLOW_LED = P1^1;
sbit GREEN_LED  = P1^2;

void delay(unsigned int ms) {
    unsigned int i, j;
    for (i = 0; i < ms; i++)
        for (j = 0; j < 123; j++);  // Adjust this value for accurate timing
}

void main() {
    unsigned char state = RED;

    while (1) {
        P1 = (P1 & 0xF8) | state;  // Update only the traffic light LEDs

        switch (state) {
            case RED:
                delay(5000);  // Red light for 5 seconds
                state = GREEN;
                break;
            case GREEN:
                delay(4000);  // Green light for 4 seconds
                state = YELLOW;
                break;
            case YELLOW:
                delay(1000);  // Yellow light for 1 second
                state = RED;
                break;
        }

        // Rotate the state using bitwise operations
        state = ((state > 2)) & 0x07;
    }
}

This implementation uses bitwise operations to efficiently update the LED states and rotate through the traffic light sequence. The state variable is updated using a combination of left shift, right shift, and AND operations, demonstrating how bitwise manipulation can create elegant and efficient state transitions.

As we conclude our journey into the secret sauce of 8051 bitwise operations, we hope you’ve gained a deeper appreciation for the power and elegance of bit-level manipulation. By mastering these techniques, you’ve unlocked a new level of control over your 8051 programs, enabling you to write more efficient, performant, and sophisticated code.

Remember, the true art of bitwise manipulation lies not just in knowing the operations, but in recognizing opportunities to apply them creatively. As you continue to develop your skills, challenge yourself to find innovative ways to leverage bitwise operations in your projects.

With practice and persistence, you’ll soon find yourself manipulating bits like a true master, pushing the boundaries of what’s possible with the 8051 microcontroller. Embrace the bitwise mindset, and watch as your code transforms into elegant, efficient solutions that stand out in the world of embedded systems programming.

In the world of microcontrollers, the 8051 family continues to be a popular choice for embedded systems developers. Despite its age, this versatile chip still finds applications in various industries due to its simplicity, reliability, and cost-effectiveness. However, to truly harness the power of the 8051, we need to optimize its performance. In this comprehensive guide, we’ll explore 10 ingenious hacks that will supercharge your 8051 projects, resulting in lightning-fast execution and improved efficiency.

One of the 8051’s unique features is its bit-addressable memory. By utilizing this capability, we can significantly reduce code size and improve execution speed. Instead of manipulating entire bytes, we can directly operate on individual bits, which is particularly useful for control applications and status flags.

SETB P1.0    ; Set bit 0 of Port 1
CLR P1.1     ; Clear bit 1 of Port 1
JB P1.2, LABEL    ; Jump if bit 2 of Port 1 is set

By using bit-addressable instructions, we can perform operations in a single cycle, leading to faster and more efficient code execution.

Efficient interrupt handling is crucial for responsive 8051 applications. To minimize interrupt latency and improve overall system performance, consider these techniques:

1. Use register banks to quickly switch context during interrupts.
2. Keep interrupt service routines (ISRs) as short as possible.
3. Use the RETI instruction instead of RET at the end of ISRs.

Here’s an example of an optimized interrupt handler:

ORG 0003H    ; External Interrupt 0 vector
LJMP EXT0_ISR

ORG 0100H
EXT0_ISR:
    PUSH PSW
    PUSH ACC
    ; Handle interrupt
    POP ACC
    POP PSW
    RETI

By following these practices, we can ensure that our 8051 responds swiftly to external events without compromising overall system performance.

When dealing with complex mathematical operations or data conversions, lookup tables can significantly improve execution speed. By pre-calculating values and storing them in program memory, we can replace time-consuming calculations with quick memory accesses.

ORG 0200H
SINE_TABLE:
    DB 0, 31, 62, 90, 116, 139, 158, 173, 185, 193, 198, 199, 197, 191, 181, 169

; Usage example
MOV DPTR, #SINE_TABLE
MOVC A, @A+DPTR    ; Load sine value into accumulator

This technique is particularly effective for trigonometric functions, logarithms, and other computationally intensive operations.

Loops are essential in many 8051 applications, but poorly implemented loops can significantly slow down execution. To optimize loop performance, consider these strategies:

1. Use DJNZ (Decrement and Jump if Not Zero) for simple counting loops.
2. Unroll small loops to reduce overhead.
3. Use self-modifying code for dynamic loop counters.

Here’s an example of an efficient loop using DJNZ:

MOV R7, #10    ; Initialize loop counter
LOOP:
    ; Loop body
    DJNZ R7, LOOP

By implementing these loop optimization techniques, we can significantly reduce execution time in iterative processes.

The 8051 offers various addressing modes, but direct addressing is often the fastest. Whenever possible, use direct addressing for frequently accessed variables to improve code efficiency.

MOV 30H, #55H    ; Direct addressing
MOV A, 30H       ; Direct addressing

Direct addressing not only reduces instruction execution time but also results in smaller code size compared to indirect addressing methods.

The 8051’s on-chip memory is significantly faster than external memory. To achieve lightning-fast execution, we should strive to keep as much code and data as possible in the internal memory. This includes:

1. Utilizing the lower 128 bytes of RAM for frequently accessed variables.
2. Using bit-addressable memory (20H-2FH) for flags and control bits.
3. Placing time-critical code in the internal ROM or RAM, if available.

By carefully managing memory allocation, we can minimize external memory accesses and dramatically improve execution speed.

Subroutines are essential for modular programming, but excessive use can lead to performance degradation. To optimize subroutine calls:

1. Use ACALL instead of LCALL for short-distance calls.
2. Consider inline code for very short, frequently used subroutines.
3. Pass parameters through registers rather than memory whenever possible.

Here’s an example of an efficient subroutine call:

ACALL SHORT_ROUTINE    ; Use ACALL for nearby subroutines

SHORT_ROUTINE:
    ; Subroutine code
    RET

By following these guidelines, we can maintain code modularity without sacrificing performance.

Conditional assembly allows us to generate optimized code for specific scenarios. By using assembler directives, we can create multiple versions of our code tailored to different hardware configurations or use cases.

#IF FAST_MODE
    MOV TMOD, #02H    ; 8-bit auto-reload timer
#ELSE
    MOV TMOD, #01H    ; 16-bit timer
#ENDIF

This technique enables us to fine-tune our code for various situations without maintaining separate source files, resulting in more efficient and maintainable projects.

Timers are crucial components in many 8051 applications. To maximize timer efficiency:

1. Use Timer 0 in Mode 2 (8-bit auto-reload) for regular interval timing.
2. Utilize the T2CON register for advanced timer control in 8052 variants.
3. Implement timer interrupts for precise timing without polling.

Here’s an example of setting up Timer 0 in auto-reload mode:

MOV TMOD, #02H    ; Timer 0, Mode 2 (8-bit auto-reload)
MOV TH0, #-50     ; Load timer high byte for 50µs interval
SETB TR0          ; Start Timer 0

By optimizing timer usage, we can achieve precise timing with minimal CPU overhead.

Data transfer operations can be a significant bottleneck in 8051 applications. To optimize data movement:

1. Use block transfer instructions like MOVX for large data transfers.
2. Implement circular buffers for efficient data queueing.
3. Utilize DMA controllers if available in advanced 8051 variants.

Here’s an example of an efficient block transfer:

MOV R0, #30H      ; Source address
MOV R1, #50H      ; Destination address
MOV R2, #10       ; Number of bytes to transfer

TRANSFER_LOOP:
    MOV A, @R0
    MOV @R1, A
    INC R0
    INC R1
    DJNZ R2, TRANSFER_LOOP

By implementing these data transfer optimizations, we can significantly reduce the time spent on I/O operations and memory transfers.

In this comprehensive guide, we’ve explored 10 genius hacks to achieve lightning-fast execution on the 8051 microcontroller. By leveraging bit-addressable memory, optimizing interrupt handling, utilizing lookup tables, and implementing efficient programming techniques, we can push the 8051 to its limits and create high-performance embedded systems.

Remember, optimization is an ongoing process. Continuously profile your code, identify bottlenecks, and apply these techniques judiciously to achieve the best possible performance in your 8051 projects. With these advanced strategies at your disposal, you’ll be well-equipped to develop efficient, responsive, and powerful 8051-based applications that stand out in the competitive world of embedded systems.

CAN protocol supports transfer of 8 bytes of data in one frame. What if you want to transfer large data? SAE J1939/21 specifications defines fragmented transmission of large data known as transport protocol (TP). TP sends message of more than 8  bytes of data in multiple packets. SAE J1939/21 specifications defines various network services, message requests and acknowledgment. it defines format of frames, sending, handshaking and reassembling of packets.

SAE J1939 TP supports sending data to global destination address (BAM) and sending data to specific  destination (CM). Data transfer part is similar in both the ways, they differ in how they start and how fast data is transferred.

SAE J1939 TP use two specific parameter groups for fragmented transmission of large data. First is transport protocol connection management message (TP.CM); it contains connection command, PGN identifier of the TP message and information about how to reconstruct the message. Second is transport protocol data transfer message (TP.DT); it contains sequence number in first byte and 7 bytes of data. A maximum of 1785 bytes can be transferred using transport protocol.

BAM TP messages are intended for complete network, so there is no handshake messages required. The sender starts with sending TP.CM message with command BAM (32) and then sender send all the data through TP.DT messages untill all data is sent. The transmitter sends all data TP.DT messages at a minimum interval of 50 ms.

• PGN: 60416 (0xEC00)
• Priority: 7
• Length: 8 bytes
• Destination: Global (255)
• Byte 1: BAM (32)
• Byte 2 and 3: Message size in bytes
• Byte 4: Number of packets
• Byte 5: Reserved (0xff)
• Byte 6 to 8: PGN

• PGN: 60160 (0xEB00)
• Priority: 7
• Length: 8 bytes
• Destination: Global (255)
• Byte 1: Sequence number (1 to 255)
• Byte 2 to 8: Data

Below example shows transmission of BAM TP messages for PGN 65260 (0xFEEC) with 17 bytes of data.

Peer to peer or CM TP contains handshaking to guarantee successful data transfer. The sender starts with a “request to send” (RTS) message. The receiver then controls the TP communication with “clear to send” (CTS) messages and finally ends TP session with “end of message acknowledge”. The data of the TP.CM Clear to Send message contains the current sequence number to transfer as well as the number of TP.DT packets allowed.  The originator then sends TP.DT messages starting at the sequence requested and stops after reaching the number of TP.DT messages allowed.  This process continues until all the data is transferred. The receiving device then has to send a TP.CM message with command byte EndofMsgACK confirming that all the data was successfully received.

• PGN: 60416 (0xEC00)
• Priority: 7
• Length: 8 bytes
• Destination: Specific
• Byte 1: RTS (16)
• Byte 2 and 3: Message size in bytes
• Byte 4: Number of packets
• Byte 5: Total number of packet sent in response to CTS.
• Byte 6 to 8: PGN

• PGN: 60416 (0xEC00)
• Priority: 7
• Length: 8 bytes
• Destination: Specific
• Byte 1: CTS (17)
• Byte 2: Max number of packets that can be sent at once. (Not larger than byte 5 of RTS)
• Byte 3: Next sequence number to start with
• Byte 4 and 5: Reserved (0xff)
• Byte 6 to 8: PGN

• PGN: 60416 (0xEC00)
• Priority: 7
• Length: 8 bytes
• Destination: Specific
• Byte 1: EndofMsgACK (19)
• Byte 2 and 3: Total message size in bytes
• Byte 4: Total number of packets
• Byte 5: Reserved (0xff)
• Byte 6 to 8: PGN

• PGN: 60416 (0xEC00)
• Priority: 7
• Length: 8 bytes
• Destination: Specific
• Byte 1: Connection abort (255)
• Byte 2 and 3: Connection abort reason
• Byte 3 to 5: Reserved (0xff)
• Byte 6 to 8: PGN

Below example shows transmission of CM TP messages for PGN 65260 (0xFEEC) with 17 bytes of data.