Rockwell Automation 1761-HHP-B30 MicroLogix 1000 with Hand-Held Programmer (HHP) - Manual (Page 285)

15 Chapter
15–1
Using Communication Protocols
This chapter contains information about communication and the message
(MSG) instruction. Specifically, this chapter contains information on:
•
types of communication
•
what the MSG instruction symbol looks like
•
typical execution time for the MSG instruction
•
how to use the MSG instruction
•
application examples and timing diagrams
Important: Only Series B or later MicroLogix 1000 HHPs and Series C or
later MicroLogix 1000 controllers support the MSG instruction.
Only Series C MicroLogix 1000 HHPs fully support Series D
functionality.
Only Series C MicroLogix 1000 HHPs will support MicroLogix
1000 analog controllers.
You cannot use the MicroLogix 1000 HHP to select or
configure DF1 half-duplex slave communications in
Series D discrete or Series A analog MicroLogix 1000
controllers.
Message Instruction
Mnemonic Function Code Name Purpose Page
MSG 200 Message
Read/Write This instruction transfers data from one node to another via the communication
port. When the instruction is enabled, the message is sent to a communication
buffer. Replies are processed at the end of scan. 15–2
Communication is the ability of a device to send data or status to other
devices. This capability typically falls into one of two categories:
initiator (master) or responder (slave). Each of these are described below:
Initiator (Master) Communication
Initiator products can begin communication processes, which includes
requesting information from other devices (reading) or sending information
to other products (writing). In addition, initiator products are usually capable
of replying to other devices when they make requests to read information.
The Series C or later MicroLogix 1000 discrete controllers and the Series A
or later MicroLogix 1000 analog controllers are in this class.
Initiator products can begin communication processes with other initiator
products (peer-to-peer communication) or with responder (slave) products
(initiator-to-responder communication).
Types of Communication