Reset & COM PIC Communication

Estimated time to complete: 7–10 minutes

This guide explains how the COM PIC is reset, how it communicates with the Main PIC (EOBC), and how it enables power lines for the transceiver and other components. This is essential knowledge for debugging boot issues and understanding startup sequencing.

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🔁 1. Reset Behavior of COM PIC

The COM PIC (Communication PIC) is automatically reset under the following conditions:

• System startup (main 5V power supplied)
• Manual reset using the external RESET button
• Software reset triggered by the EOBC or UART command

On reset, the COM PIC initializes UART interfaces, sets internal flags, and enables relevant powerlines as part of startup.

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🔌 2. Powering the Powerlines

After reset, the COM PIC powers the necessary EPS (powerlines) using GPIO control:

Line	Description	Controlled By
5V_RF	Powers the RF front-end / transceiver	COM PIC GPIO
3V3_RF	Powers logic-level devices on RF board	COM PIC GPIO
5V_GPS	(If available) powers GPS module	COM PIC GPIO

Logic sequence:

On boot → COM PIC sets GPIO HIGH → EPS regulator enables → voltage applied

⚠️ If no power appears on RF board, check GPIO state using logic analyzer or multimeter.

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📡 3. Communication With Main PIC (EOBC)

COM PIC communicates with the EOBC via UART.

UART Parameters:

Parameter	Value
Baud rate	9600 or 19200
Data bits	8
Stop bits	1
Parity	None

Message Structure:

All commands use a 3-byte fixed format:

Byte 1: Start byte (0xA0)
Byte 2: Command ID
Byte 3: Payload/Argument (optional, 0x00–0xFF)

Example Commands:

Command	ID	Purpose
Reset COM PIC	0x00	Soft-reset from EOBC
Send CW	0x01	Request beacon transmission
RF Enable	0x02	Turn on RF module

Example:

uint8_t cmd[] = { 0xA0, 0x02, 0x01 }; // Turn on RF module
send_uart(COM_UART, cmd, 3);

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🔁 4. COM PIC Command Acknowledgement

On receiving a command, the COM PIC may respond with:

• 0xB0 for ACK
• 0xB1 for NACK
• Followed by a status code or data byte

Example:

[0xB0][0x02] → ACK for RF Enable

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🗺️ 5. System Flow Diagram

sequenceDiagram
    participant EOBC
    participant COM_PIC
    participant EPS
    participant TRX

    EOBC->>COM_PIC: UART (0xA0 0x02 0x01) RF ON
    COM_PIC->>EPS: Set GPIO HIGH (5V_RF)
    EPS->>TRX: Power ON
    COM_PIC-->>EOBC: ACK (0xB0)

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✅ 6. Summary

• COM PIC resets on startup and enables powerlines
• It uses UART to receive commands from EOBC
• Controls EPS lines via GPIO
• Uses simple 3-byte command structure
• Sends ACK/NACK responses to confirm action

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🧪 7. Useful Debug Tips

Issue	Check
RF not powering on	Confirm 5V_RF GPIO high
No ACK response	Verify UART pins and baud rate
Reset loop	Power instability or brownout
No command effect	Wrong command ID or byte order

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Need more help? Contact your COM PIC lead or refer to the Command Reference Sheet.

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Would you like me to generate a diagram showing GPIO-to-powerline mapping or UART lines between EOBC and COM PIC?