Bradley Smoker PLC-5 user manual Method Option Name Principal Benefits

10-4Communicating with Devices on a Serial Link

Master Station to Remote Station Communication Methods

A PLC-5 master station can communicate with remote stations in two ways:

Method	Option Name	Principal Benefits
initiating polling packets to remote stations	standard	This is the communication mode used most
according to their position on a polling list	communication mode	often in point-to-multipoint configurations.
Polling packets are formed independently		Provides for these capabilities:
of any user-programming.		remote stations can send messages to the
		master station (polled report-by-exception)
		remote stations can send messages
		to each other
		lets the master station maintain an active
		node table
		The poll list resides in a user designated and
		accessible integer-type data file. You can:
		include the master on the poll list
		configure the master for between-station polls
		(master transmits any message that it needs to
		send before polling the next remote station)
		have the master both in the poll list and
		configured for between-station polls
initiating communication to remote stations	message-based	If your application uses satellite transmission or
using only user-programmed message	communication mode	public switched telephone network
(MSG) instructions		transmission, consider choosing
		message-based. Communication to a remote
Each request for data from a remote station		station can be initiated on an as needed basis.
must be programmed via a message
instruction.		Or choose this method if you need to
		communicate with non-intelligent remote
The master polls the remote station for a		terminal units (RTUs).
reply to the message after waiting a
user-configured period of time. The waiting
period gives the remote station time to
formulate a reply and prepare the reply for
transmission. After all of the messages in
the master’s message-out queue are
transmitted, the remote-to-remote queue is
checked for messages to send.

Publication 1785-UM012D-EN-P - July 2005