[Solved] You want to extend a serial protocol to include a command byte after the start byte and before the payload.... How would you modify the message structure and checksum calculation? | Raspberry Pi

Raspberry Pi - Serial UART Communication

You want to extend a serial protocol to include a command byte after the start byte and before the payload. The start byte is 0x01, command byte is 1 byte, payload is variable length, and end byte is 0x04. How would you modify the message structure and checksum calculation?

AMessage = start + payload + command + checksum + end; checksum covers entire message including start and end

BMessage = start + command + payload + end + checksum; checksum covers command and payload

CMessage = command + start + payload + checksum + end; checksum covers payload only

DMessage = start + command + payload + checksum + end; checksum covers command and payload bytes only

Step-by-Step Solution

Solution:

Step 1: Define message structure with command byte
Start byte first, then command byte, then payload, checksum, and end byte last.
Step 2: Determine checksum coverage
Checksum typically covers command and payload to detect errors in data, excluding framing bytes.
Final Answer:
Message = start + command + payload + checksum + end; checksum covers command and payload bytes only -> Option D
Quick Check:
Checksum excludes framing bytes, includes command and payload [OK]

Quick Trick: Checksum covers command and payload, not start/end bytes [OK]

Common Mistakes:

MISTAKES

Including start/end bytes in checksum
Placing checksum after end byte
Mixing order of command and payload

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How would you modify the message structure and checksum calculation?

Step 1: Define message structure with command byte

Step 2: Determine checksum coverage

Final Answer:

Quick Check:

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