User`s guide

Copyright © 2004 EIM COMPANY, INC. • 13840 PIKE ROAD • MISSOURI CITY, TX. 77489
Page 25
Controlinc 1746-C (Version 5.21) Network Master Users Guide (2004-11-18)
The interfacing between the PLC and the 1746-C is performed in the 1746-C module in a section of
RAM that is used as an exchange buffer area. To prevent potential overwriting problems when
performing transfers, there are two separate buffers in this exchange area:
• M0 file … Basic Input Buffer (BIB): PLC fills to send 64 words to the 1746-C.
• M1 file … Basic Output Buffer (BOB): 1746-C fills to send 64 words to the PLC.
This is the only address accessed by the PLC when executing the M0/M1 transfer commands (meaning
that all reads & writes by the PLC are to and from these buffers).
Figure 3-1 Concept Diagram of Command Operations
1746-C
Standard RAM
(Tables)
1746-C driver
o
p
erations
MODBUS RTU
commands
executed by the
1746-C and
actuators
ACTUATOR
M1 File Transfer
commands
executed by the
1746-C
PLC must read the
M1 file in timely
manner as to not
slow down networ
k
scanning
PLC
64-Word M1 File Transfer
B
u
ff
e
r
(
B
O
B
)
M0 File Transfer
commands
executed by the
PLC
The PLC must ensure
the M0 file is there fo
r
the 1746-C to read in
a timely enough
manner as to not
slow down network
scanning
The 1746-C looks
for an M0 file
transfer at the start
of the PLC Interface
time slice
PLC
64-Word M0 File Transfer
B
u
ff
e
r
(
BIB
)