Carel refrigeration controllers have the following features of the implementation of the communication interface:

The modules often do not have an integrated RS-485 driver, and the connection must be made to the TTL serial bus port via TTL-RS485 converter. The default transmission format - 19200, 8 data bits, no parity, 2 stop bits. To get net address in PDU add 0x30 the controllers address.

New models have Modbus RTU, while older models have a proprietary Carel communication protocol. The protocol is quite efficient one, becuase it only sends changes of its parameter, or “no changes” telegram. So the host syncronize its variable once and the gets updates.