This extension is almost identical to the RS232 extension, but even simpler. The RS485 is different from an RS232 mainly by having to enable/disable TX/RX, because the serial lines are a bus.
| Command | Phase | Dir | B0 | val16 | val32 | Description |
|---|---|---|---|---|---|---|
| 0x69 | Start | S→E | config | B1=end character, B2=unused | baud rate | Configure the RS485. config bits 0-1:word length (0:5, 1:6, 2:7, 3:8), bit 2-5: parity (1:even, 2:odd, 3:zero, 4:one), bit 6:stop bits (0:1, 1:2), bit 7:has end character flag |
| 0x71 | S→E | Send bytes (see below) |
Sending up to 255 bytes works as follows:
- Send
0x71withB0=0x00.B1= length of byte stream,B2= CRC8 over the byte stream,B3…B6: first 4 bytes of the package - Send
0x71with(B0 * 6 - 2)being the offset into the byte stream.B1…B6are the next 6 bytes of the package
Once the last package necessary is received and the CRC8 is validated, they package is queued for sending. If the CRC8 is not correct, the package is simply ignored.
If an end character is set (e.g. CR), then all received bytes are buffered till this character is detected or the 512 bytes receiving buffer is full. The are send back as a 0x44 fragmented package (see the description in the general legacy extension document) with the type being 0x0A (RS232 data bytes received).
Without an end character, bytes are send whenever they are available with a little delay to allow avoid sending individual bytes all the time.