The ACM5004/5508-2-I support multiple signaling protocols (RS-232, RS-422 and RS-485) on the serial RJ-45 ports 1 through 4/8.
- For RS232 they have the Cisco pinout
- For RS-422 mode it’s 4-wire full duplex transmit on TX+/TX- pair, receive on RX+/RX- pair with the following pinout:
- For RS-485 it’s 2-wire half duplex. For the RS-485 option, to provide half duplex ‘party-line’ communications over a 2-wire bus (D+/D-), two short cable loops are required between the RX+/TX+ pins (pins 1 and 6) and RX-/TX- pins (pins 3 and 8) on the serial RJ-45 cable connector. This is because the ACM5004-2-I uses universal differential transceivers that support 4-wire (RS-422) and 2-wire (RS-485) operation.
In RS-485 mode, the ACM5004/5508-2-I listens on the 2-wire bus for receive data until it is required to send data. In RS-485 send mode it stops receiving, enables its transmitters when there is data to be sent, transmits the data and returns to receive mode. This eliminates the possibility of collisions with other devices which share the RS-485 bus and avoids receiving bogus stale echoed data.