Both PC1001-A3 and PC1002-A3 Cerberus PACE Compact digital audio matrix boards provide 4 'PACE-Bus' (RS485) connectors ('1-RS485' to '4-RS485') in the options area. These connectors can be used to connect the 'PACE-Bus' (RS485) operating terminals and the 'PACE-Bus' (RS485) call stations.