Allen-Bradley PLC-5 User Manual page 153

In system mode, you can send data to a device using:
All data is encapsulated inside a DF1 protocol packet; therefore, the controller
can communicate only with peripheral devices that support the DF1 protocol.
Examples of DF1 peripheral devices are:
Use this Mode For
communication between a PLC-5 controller and one other DF1 protocol compatible device
Point-to-Point
In point-to-point mode, a PLC-5 controller uses DF1 full-duplex protocol.
DF1 Master Mode control of polling and message transmission between the master and each remote node
In master mode, a PLC-5 controller uses DF1 half-duplex polled protocol.
The master/remote network includes one PLC-5 controller configured as the master node and
up to 254 remote nodes. You link remote nodes using modems or line drivers.
A master/remote network can have node numbers from 0 to 376 (octal). Node 377 is reserved
for broadcast. Each node must have a unique node address. Also, at least 2 nodes must exist
to define your link as a network (1 master and 1 remote station are two nodes).
DF1 Slave Mode using controller as a remote station in a master/slave serial communication network
When there are multiple remote stations on the network, you link remote nodes using
modems or line drivers. When you have a single remote station on the network, you do not
need a modem to connect the remote station to the master; you can configure the control
parameter for no handshaking. You can connect from 2 to 255 nodes to a single link. In slave
mode, a PLC-5 controller follows DF1 half-duplex protocol.
One node is designated as the master and it controls who has access to the link. (For
example, a master can be a PLC-5/250 or PLC-5/40 controller or a computer running
ControlView SCADA option software. All other nodes are remote stations and must wait for
permission from the master before transmitting. The master (except PLC-5/250) can send and
receive messages from all nodes on the link and to nodes on other Data Highway links
connected to the multidrop; whereas, a remote station can only respond to the master.
the message (MSG) instruction; or
ASCII write instructions (send as an ASCII string)
personal computers
communication modules such as 1771-KF2 series C, 1771-KE,
1771-KF, and 1785-KE
modems
Communicating with Devices on a Serial Link
Publication 1785-UM012D-EN-P - July 2005
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