Publication 1766-RM001A-EN-P - October 2008
Protocol Configuration 593
DF1 Half-Duplex
Protocol
DF1 Half-Duplex protocol provides a multi-drop single master/multiple
slave network. In contrast to the DF1 Full-Duplex protocol,
communication takes place in one direction at a time. You can use the
RS-232 port on the MicroLogix controller as both a Half-Duplex
programming port, and a Half-Duplex peer-to-peer messaging port.
MicroLogix 1400controller supports Half-Duplex modems using RTS/CTS
hardware handshaking.
DF1 Half-Duplex supports up to 255 devices (addresses 0…254, with
address 255 reserved for master broadcasts). Note: When configuring a
message instruction, set the target node address to -1 for broadcast
messages.
Broadcast messages are handled as follows:
DF1 Half-Duplex Master Driver Broadcast Messages
A broadcast write command initiated by the DF1 half-duplex master is
received and executed by all DF1 half-duplex slaves. A broadcast write
command received by the DF1 half-duplex master after polling a DF1
half-duplex slave is received, acknowledged and re-broadcast without
being executed by the DF1 half-duplex master. It is treated like any other
slave-to-slave command, except that no acknowledgement is expected
after re-broadcast.
DF1 Half-Duplex Slave Driver Broadcast Messages
When a broadcast write command is initiated by a DF1 half-duplex slave,
it is queued up just like any other MSG command until it receives a poll
from the DF1 half-duplex master. After transmitting the broadcast write
command, the DF1 half-duplex slave receives an acknowledgement that
the DF1 half-duplex master received the packet without error. When the
DF1 half-duplex master re-broadcasts the broadcast write command, the
initiating DF1 half-duplex slave receives and executes the command along
with all of the other slave nodes receiving the broadcast packet. No
acknowledgement or reply is returned.
Choosing a Polling Mode for DF1 Half-Duplex Master
A master station can be configured to communicate with slave stations in
either Message-based polling mode or Standard polling mode. The pros
and cons of each polling mode are described below.
efesotomasyon.com - Allen Bradley,Rockwell,plc,servo,drive
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