Rockwell Automation 2705 RediPanel Push Button Module - Manual (Page 54)

Chapter 4
Programming the RediPANEL Modules
4–15
Use a 1771-SN Sub I/O Scanner with a PLC-5 processor when the
application requires more remote devices than the processor can
accommodate. The Sub I/O Scanner module can communicate to 16
additional remote I/O devices. Locate the 1771-SN Sub I/O scanner in the
same rack as the PLC-5 (the local rack) or in anyone of the remote racks
supported by the processor.
The PLC-5 communicates with the Sub I/O Scanner using block transfer read
and write instructions. The block transfer read instruction reads input data
from the Sub I/O Scanner and transfers that data to integer files in the PLC.
The block transfer write instruction writes output data to files in the PLC,
then transfers that data to the Sub I/O Scanner. Input and output addresses
begin at the integer file assigned to the block transfer instruction (instead of
Input addresses starting with “I” and Output addresses starting with “O”).
The rest of the input addresses depend on the specific integer file designated
as the Data File in the block transfer read instruction. The rest of the output
address depends on the specific integer file designated as the Data File in the
block transfer write instruction.
Figure 4.5 an example of a bidirectional block transfer between a Sub I/O
Scanner and a PLC-5.
Figure 4.5
PLC-5 Block Transfer
( EN )
( DN )
( ER )
BLOCK TRNSFR READ
RACK
0
GROUP 7
MODULE 1
CONTROL BLOCK N10:0
DATA FILE N11:0
LENGTH 20
CONTINUOUS N
N10:0
]
/
[
15
N10:5
]
/
[
15
BTR
Enable Bit
BTW
Enable Bit
Read from Sub-Scanner to the PLC-5 .
N10:5
]
/
[
15
N10:0
]
/ [
15
BTW
Enable Bit
BTR
Enable Bit
Write to the Sub-Scanner from the PLC-5 .
( ER )
( DN )
BTR
( EN ) BLOCK TRNSFR WRITE
RACK
0
GROUP 7
MODULE 1
CONTROL BLOCK N10:5
DATA FILE N12:0
LENGTH 20
CONTINUOUS N
BTW
Using a PLC-5
with a Sub I/O Scanner