When the MCM driver is setup to be a Modbus master, the firmware will maintain a list of status codes. Each number in the "master commman error" list corresponds to a single message in the master command list. The position of a given status code matches the position of the associated message in the list. This list can be accessed using hyperterminal and connecting the computer to the configuration or debug port on the module. From the main menu, look for the "command error list". Any non-zero value in this list indicates that there is a communications error. Since each message in the list is limited to communications with one slave, then the status of a command in the list will indicate that a particular slave may be failing. Note that this list can be brought into the ladder logic by using the "command error pointer" to place this table in the read register area of the module.