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Serial protocol checklist for a laser rangefinder module
Twelve things a protocol document must state. Send this list to any supplier; the ones who can answer all twelve have shipped the product to integrators before. The ones who answer six have not.
| Transport and wiring | RS-422, RS-232, UART-TTL or CAN; signal levels; required common ground; maximum cable length; whether the idle state is defined. |
|---|---|
| Baud rate and framing | Nominal rate and its tolerance; data bits, parity, stop bits; whether the module tolerates a host that opens at a different rate first. |
| Message envelope | Start bytes, length field endianness, command byte, payload layout, terminator. A document that omits endianness is not a protocol document. |
| Checksum or CRC | The polynomial, the seed and exactly which bytes are covered. Ambiguity here produces intermittent rejections that no one can debug on site. |
| Command set | At minimum: single measurement, continuous mode with rate, stop, read status, read serial number and firmware version. |
| Error and status codes | Every code, what causes it, and whether it clears itself. Include the 'no return' and 'ambiguous return' cases explicitly. |
| Timing | Measurement duration per mode; the minimum interval between commands; what the module does if a command arrives mid-measurement. |
| Streaming format | If continuous mode exists, the record layout, the rate tolerance and how the host resynchronises after a dropped byte. |
| Startup and reset | Time to first valid measurement; behaviour on power interruption; whether settings persist across power cycles. |
| Configuration writes | Which parameters are writable, their ranges, and whether a write is acknowledged, echoed or silent. |
| Versioning | A protocol version field, and a policy for what changes between versions. |
| Example exchange | At least one complete hex transcript of a request and its reply. This single item saves the most integration time of anything in the document. |
Why this list exists
Integrations rarely fail on the laser. They fail on framing, endianness and checksum coverage — three things that are invisible in a brochure and expensive to discover in the field. A supplier who publishes a complete protocol document is telling you something about how they work, not just about their module.
Want a protocol document for a specific model?
Send the model code; the interface document comes back with it.
Email tommy@erdimail.com
The questions to ask first
This checklist is generic engineering guidance, not a description of any specific ERDI protocol. Interface documents are supplied per model.