Rockwell Automation 1771-DMC_DMC1_DMC4_DXPS Control Coprocessor User Manual - Manual (Page 69)

Chapter 5
Developing Programs
5-9
This section defines the MSG functions that process unsolicited messages
from a PLC-5 programmable controller. See Appendix B, Application
Program Interface Routines, for more information.
Read/Write MSG Functions
Use read/write MSG functions to process unsolicited MSG instructions
from a PLC-5 ladder-logic program. See Table 5.G.
Table 5.G
ControlĆCoprocessor MSG Read/Write Processing Functions
Function What It Does Why You Need It When You Use It
MSG_READ_W_HANDLER Processes an unsolicited PLCĆ5
MSG read instruction
To perform synchronous
processing of an unsolicited
PLCĆ5 MSG read instruction
When you want to transfer read data to
the PLCĆ5 programmable controller
before the next step of the application
program is executed
MSG_READ_HANDLER Initiates processing of an
unsolicited PLCĆ5 MSG
read instruction
To perform asynchronous
processing of an unsolicited
PLCĆ5 MSG read instruction
When you want to transfer read data to
the PLCĆ5 programmable controller but
return controlto the application program
before the message is executed (also,
see MSG_WAIT function)
MSG_WRITE_W_HANDLER Processes an unsolicited PLCĆ5
MSG write instruction
To perform synchronous
processing of an unsolicited
PLCĆ5 MSG write instruction
When you want to receive write data
from the PLCĆ5 programmable controller
before the next step of the application
program is executed
MSG_WRITE_HANDLER Initiates processing of an
unsolicited PLCĆ5 MSG
write instruction
To perform asynchronous
processing of an unsolicited
PLCĆ5 MSG write instruction
When you want to receive write data from
the PLCĆ5 programmable controller but
return controlto the application program
before the message is executed (also,
see MSG_WAIT function)
When a PLCĆ5 programmable controller generates a Message READ instruction, a corresponding MSG_READ_HANDLER or
MSG_READ_W_HANDLER function must be used by the control coprocessor to handle the request. When a PLCĆ5 programmable controller
generates a Message WRITE instruction, a corresponding MSG_WRITE_HANDLER or MSG_WRITE_W_HANDLER function must be used by the
controlcoprocessor to handle the request.
When a PLC-5 programmable controller initiates an unsolicited read/write
MSG instruction, use read/write MSG functions in the control coprocessor
for transferring small amounts of data between the programmable
controller and the control coprocessor. The maximum size that you can
specify for the buffer in the read/write MSG function is 240 bytes for a
read and 234 bytes for a write.
For transferring larger amounts of data between the programmable
controller and the control coprocessor, use a read/write MSG function in
conjunction with a read/write DTL function in your control-coprocessor
program. You can transfer up to 1,000 words between the control
coprocessor and a PLC-5 programmable controller using the read/write
DTL function.