Rockwell Automation DAG6.5.8 APPLICATION GUIDE SCADA SYSTEM - Manual (Page 61)

Publication AG-UM008C-EN-P - February 2005
Configuring Enhanced PLC-5 Processors 2-23
Messaging Messaging can occur between:
•
a master station and a slave station
•
a slave station and its master station
(See Polled Report-by-Exception)
•
slave stations or between two processors connected via a
point-to-point link
Master Station to Slave Station
A PLC-5 master station communicates with the slave stations that are
connected to it via modems in a point-to-multipoint configuration. A
master station sends a slave station messages to receive status or issue
commands. For sample messaging ladder logic, see page E-8.
Polled Report-by-Exception
Slave stations can gather information from the I/O points they are
responsible for and can send any anomalous readings to the master
station. To do this, write ladder logic in the slave station to monitor
certain conditions and send the data in a MSG instruction to the
master station. Figure 2.6 is an example MSG instruction and control
block that a PLC-5 processor in a slave station can send to a PLC-5
master station. For sample messaging ladder logic when using a PLC-5
as a slave, see page E-12.
Inquiry Sent word 4 The number of ENQs sent by the processor
Bad Packet/No ACK word 7 The number of incorrect data packets received by the processor for which
a NAK was returned
DTR (Data Terminal Ready) word 0;bit 4 The status of the DTR handshaking line (asserted by the processor)
DSR (Data Set Ready) word 0;bit 2 The status of the DSR handshaking line (received by the processor)
RTS (Request to Send) word 0;bit 1 The status of the RTS handshaking line (asserted by the processor)
CTS (Clear to Send) word 0;bit 0 The status of the CTS handshaking line (received by the processor)
DCD (Carrier Detect) word 0;bit 3 The status of the DCD handshaking line (received by the processor)
Status Field Diagnostic File Location Definition