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LoxoneLinkLegacyExtensionRS232.md

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RS232 Extension (0x06)

This extension is almost identical to the RS485 extension, but with the additional checksum validation.

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)
0x7C Start S→E Additional configuration: B0:=!0 =>ACK is defined, B1:=!0 =>NAK is defined, B2:ACK byte, B3:NAK byte, B4:checksum mode

Sending bytes

Sending up to 255 bytes works as follows:

  1. Send 0x71 with B0 = 0x00. B1 = length of byte stream, B2 = CRC8 over the byte stream, B3…B6: first 4 bytes of the package
  2. Send 0x71 with (B0 * 6 - 2) being the offset into the byte stream. B1…B6 are 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.

Receiving bytes

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.

In addition to the RS485 extension, the RS232 allows checksum validation. This happens after receiving, before sending the bytes to the server. If the checksum mode is not none, it validates the checksum and either sends an ACK (if enabled) or a NAK (if enabled), depending on a valid checksum or not.

The following checksum modes exist:

Value Mode Description
0 None No checksum active
1 XOR The last byte of the package has to be the XOR value of the bytes before
2 Sum The last byte of the package has to be the 8-bit sum value of the bytes before
3 CRC8 The last byte of the package has to be the CRC8 of the bytes before
4 Modbus The last word has to be the CRC16-Modbus of the bytes before
5 Fronius The package format is 0x80, 0x80, 0x80, data-bytes, sum (see Sum above, but without the 3-byte header)