Momentum Sales & Marketing Modbus Plus 170 PNT Series - Manual (Page 33)

Communication Adapter Message Handling
870 USE 103 00 May 2001 33
How Messages are Transacted
Overview This section explains how a Communication Adapter relays information between its
I/O base and a programmable controller.
The Right to
Transmit A token frame is passed from node to node in a rotating address sequence. The
node currently holding the token has the sole right to transmit. All other nodes
monitor the network and extract messages addressed to them.
Messages from
Communication
Adapters When a Communication Adapter at an input base module acquires the token, it
transmits its message to the programmable controller node. The message data
describes the current states of the signals at the base’s field input terminals.
The controller reads the message and steers its contents into the data registers
defined for that adapter’s address in the controller’s Peer Cop table.
Messages to
Communication
Adapters When the programmable controller acquires the token, it transmits its messages to
the Communication Adapters. Messages are sent to the node addresses defined in
the controller’s Peer Cop table, with the message contents taken from the data
registers defined in the table.
Each Communication Adapter at an Output base module uses its received message
to control the field devices connected to the base’s output terminals.