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18. What is the RS485 protocol used on Monicon's controllers?
The RS485 protocol used on Monicon's controllers is designed for simplicity and reliability.
The RS485 communication interface allows the slave unit (i.e. control module) to be interrogated and some options programmed by a remote computer. Up to 100 units may be connected to the same RS485 interface.
Each unit operates in polled slave mode. This means that the unit cannot initiate a communication, it can only respond when addressed by the master computer. The master computer broadcasts an address, a command code, a variable field and a checksum. The addressed slave unit then responds with its identification, a response identifier, a variable field and a checksum.
To reduce the effect of interference from external electrical signals the RS485 interface uses a differential signal over a “twisted pair” cable. To further reduce the effects of interference, a low Baud rate of 2400 (or 1200) Baud is used. Finally, each communication is accompanied by a checksum. The use of a checksum ensures that if data corruption does occur, the information is disregarded and the information is transmitted again.