Rockwell Automation 1771-DMC_DMC1_DMC4_DXPS Control Coprocessor User Manual - Manual (Page 66)

Chapter 5
Developing Programs
5-6
The control coprocessor communicates with a standalone-mode
programmable controller using backplane-interface (BPI) functions. The
communication is via the 1771 I/O chassis backplane. You can also use
the BPI functions when you have a PLC-5 programmable controller
directly connected to the control coprocessor.
For backplane communication, the control coprocessor appears to the
programmable controller as a 16-bit, bidirectional I/O module. The control
coprocessor can perform both discrete- and block-data transfers.
Important: The only bits available for use by the application program
are the upper 8 bits (10-17). The lower 8 bits (0-7) are reserved for
block transfer, even if there are no block transfers programmed to the
control coprocessor.
You must prepare a control-logic program in the programmable controller
to initiate block transfer and/or discrete reads and writes with the control
coprocessor. See page 5-21 for an example of a control-logic program.
ATTENTION: The control coprocessor will not communicate
via discrete or block transfer in any chassis (remote or local) set
for 2-slot addressing; however, 1-slot and 1/2-slot addressing
are valid configurations for a chassis that contains a control
coprocessor communicating via discrete or block transfer with a
PLC processor.
Update Discrete Data
Use BPI_DISCRETE to get the updated output-image word from the
PLC-5 programmable controller or send the input-image word to the
controller. The function determines whether it is an input or an
output word.
Accomplish BlockĆTransfer Reads and Writes
Use BPI_WRITE and BPI_READ routines to allow PLC-5 programmable-
controller reads and writes of block data across the backplane interface.
Function What It Does
BPI_WRITE This routine interfaces with a synchronous blockĆtransfer read from a programmable controller
BPI_READ This routine interfaces with a synchronous blockĆtransfer write from a programmable controller
Howto Use BPI Functions