Page D-1
MPS Motor Protection System Rev. 6-F-022117
Appendix D, MPS A-B DF1 Protocol
APPENDIX D
MPS A-B DF1 PROTOCOL
D.1 PROTOCOL
The MPS A-B
®
Protocol is based on the half-duplex
master/slave Allen-Bradley (A-B) Data Highway Protocol
(DF1) as described in Allen-Bradley Bulletin 1770-6.5.16
October 1996. This publication is available from the A-B
web site at www.ab.com.
The communications system consists of a single master
and up to thirty-two slaves connected to a 2-wire
RS-485 multi-drop network. MPS Control Units are slave
devices on this network.
If the master does not have an RS-485 port, an RS-232
to RS-485 converter is required. The RS-485 converter
should have automatic send-data control (SD). SD
control does not require handshaking lines since it uses
the data line to control the RS-485 transmitter. The
SE-485-DIN converter is recommended. It includes
optical isolation and baud rate selections from 9,600 to
57,600 bits per second. For additional information on
converters, see Technical Information TI 9.9.
The MPS supports the DF1 commands shown in
Table D.1. Each PLC has limitations when using a
particular command. Determine the best command to use
for a particular application.
TABLE D.1 DF1 COMMANDS
The PLC-5 and SLC 500 support reading and writing to
integer files (Type N) and float files (Type F). Since
MPS meter values are float types, these will typically be
stored in a PLC Type-F file. It is also possible to read
float types from the MPS as two integers; however,
further processing is required to obtain the float value.
The PLC requires two communication ports—a PLC
programming port and an MPS communications port.
Typically, a DH+ port will be used for PLC programming
and the RS-232 port is used for MPS communications via
an SE-485-DIN converter.
A-B
®
is a registered trademark of Rockwell International
Corporation.
D.2 PLC-5 / SLC 500 CHANNEL-0 SETUP
The RS-232 Channel-0 port is set up for a DF1 half-
duplex master. Set the Channel-0 baud rate and CRC to
match the MPS settings. The parity bit is not supported
on the MPS. Where applicable, set Reply Message Wait
to 100 ms.
Additional recommended PLC settings:
DF1 Retries = 3
RTS Send Delay = 1 (20 ms)
RTS Off Delay = 0
Ack timeout = 5 (100 ms)
Reply msg wait = 3 (60 ms)
For the polling mode, select MESSAGE BASED (DO
NOT ALLOW SLAVE TO INITIATE MESSAGES) or
STANDARD (MULTIPLE MESSAGE-TRANSFER
PER NODE SCAN). The MPS can buffer up to 3
messages. The selection MESSAGE BASED (DO NOT
ALLOW SLAVE TO INITIATE MESSAGES) is
recommended.
D.3 TYPED-READ
The Typed-Read message is used to read data from the
MPS. The Typed-Read message requires a Control Block
where the message configuration is stored. In the SLC,
this is normally N7:0 but could be any other file that
supports the control-block data. Use the following MSG
settings:
Read/Write: Read
Target Device: PLC5 of SLC for SLC500 or Control
Logix
Local/Remote: Local
Control Block: N7:0
NOTE: For the PLC-5, the message block must be of type
MG so that the channel number can be set in the message
setup screen.
The Setup screen is used to specify file information. In
the This Controller section, Data Table Address is the
destination in the PLC where data is to be stored. This
can be a float (Fx:x) file or an integer (Nx:x) file.
Element Size must be set to the number of elements to
transfer. This is a decimal value and this value is limited
in some controllers. In the SLC 500, the maximum value
for integers is 100 and for floats it is 50.
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