Rockwell Automation 1770, D17706.5.16 Ref Mnl DF1 Protocol Command - Manual (Page 39)

3–2 Using Half-duplex Protocols to Send and Receive Messages
Publication 1770Ć6.5.16 - October 1996
Half-duplex protocol:
•
is a multidrop protocol for one master and one or more slaves
•
provides a lower data throughput than full-duplex
•
allows communication with each node on the multidrop link
•
allows communication with nodes on links connected to the
multidrop link
If the master is programmed to relay messages, then nodes on the
multidrop can engage in virtual slave-to-slave transfers. Half-duplex
protocol operates on a multidrop link with all nodes interfaced
through half-duplex modems. There may be from 2 to 255 nodes
simultaneously connected to a single link.
In half-duplex mode, one node is designated as master and it
controls which node has access to the link. All other nodes are
called slaves and must wait for permission from the master before
transmitting. Allen-Bradley devices with master and slave
capabilities include:
Devices with master capability Devices with slave capability
• SLC 5/03 and 5/04 (on channel 0) À • 1747ĆKE
• 1771ĆKGM DH SCADA Master module • 1770ĆKF2, ĆKF3, ĆKFC
• 5130ĆRM1, ĆRM2, ĆKA (channel 1) • 1775ĆKA (via modem port)
• 5130ĆRM2 • 1785ĆKE
• a userĆprogrammed intelligent device • 1771ĆKE, ĆKF, ĆKG
• a personal computer running ControlView
software
• PLCĆ5/11 Ć5/20, Ć5/30, Ć5/40, Ć5/60,
PLCĆ5/80 (on channel 0)
• PLCĆ5/11 Ć5/20, Ć5/30, Ć5/40, Ć5/60,
PLCĆ5/80 (on channel 0)
• SLC 5/03 and 5/04 (on channel 0)
• personal computer running
WINtelligentt LINXt software
• 5130ĆRM1, ĆRM2, ĆKA (channel 1)
• personal computer running RSLINXt
• personal computer running
WINtelligentt LINXt software
• personal computer running RSLINXt
À SLC 5/03 and 5/04 processors (OS302 and OS401, respectively) now support halfĆduplex DF1
masters.
With half-duplex protocol, you can use a:
•
two-circuit system – master sends and slaves receive on one
circuit, slaves send and master receives on the other
•
one-circuit system – master and slaves send and receive on the
same circuit
HalfĆduplex Protocol Message
Transmission