...
| Byte | Field Name | Description |
|---|---|---|
| 0 | Start of Frame | Fixed value of 0xF1; will be referred to as START_OF_FRAME throughout this document. |
| 1 | Primary Header | Defines the primary frame type. These are listed in /wiki/spaces/SPRC2/pages/110562985. |
| 2 | Secondary Header | Identifies the command subset of the given primary frame type. These are listed in /wiki/spaces/SPRC2/pages/110562985. |
| 3 | Frame Sequence Number | 0 – 127: Host initiated transactions 128 – 255: Module initiated transactions The Frame Sequence Number enumerates a serial message exchanged between the Host and the Module, and vice versa. Use of a Frame Sequence Number for each such message is recommended. For best practice, we also recommend the Frame Sequence Number be incremented by 1 for each newly initiated message. Any transaction, whether initiated by the Host or the Module, may be acknowledged (i.e., ACK'ed) by the recipient with a response using the same Frame Sequence Number. The Frame Sequence Number is used for tracking purposes but is not a mandatory feature. If its use is not desired, it should be assigned a value of 0x00. |
| 4 | Payload Length | Defines the length of the payload of a received or transmitted frame as 0-n bytes; at the time of this writing, the maximum acceptable values for n are:
Received by Module – 0x7A or 122 bytes |
...