The SST™ Communication Module connects Rockwell SLC 500 PLCs as a Master or Slave to scan or emulate PROFIBUS DP I/O. With the user-defined data space of 2064 bytes Input and 2064 bytes Output, the SST™ Profibus module provides a cost-efficient solution to connect SLC CPUs with large PROFIBUS networks. A 9-pin serial port included on the scanner allows for firmware upgrades in the field and the upload of I/O configurations. The SLC's processor logic scan and the PROFIBUS I/O scan are independent of each other. The SLC processor reads the scanner input data during its input scan and writes the output data during its output scan. The scanner reads input data from the Slaves and writes output data to the Slaves independent of what the SLC is doing. Slave status, diagnostic status information on all Slaves, network diagnostic counters and DP Master diagnostic counters are maintained by the scanner. The scanner does not require the set-up of a G-file in the SLC.