Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 123)

Calculating Program Timing
Chapter 9
9-6
Remote I/O and Processor-Resident I/O
The processor performs block transfers asynchronously to the program
scan. The processor also interrupts the program scan asynchronously to
momentarily access BTW and BTR data files. The processor performs one
remote block transfer per addressed rack and per remote I/O scan.
Figure 9.2 shows timing loops for block transfer from a Classic PLC-5
processor.
Figure 9.2
Transferring Block Data to Local and Remote I/O
Rack 7
Processor
Rack 0
Remote I/O
Scan
Remote I/O
Program
Scan
Rack 6
Rack 5
One transfer per
I/O scan
One transfer per
I/O scan
One transfer per
I/O scan
BTR or BTW Data
BT
Requests
Q
A
BTR or BTW Data
BT Requests
Q
A
BTR or BTW Data
BTRequests
Q
A
BTR or BTW Data
BT
Requests
Q
A
Q = Queue
A = Active
Buffer
I/O Scan
Multiple
Block Transfers
Q
A
One transfer per
I/O scan
BTR or BTW Data
¶
The adapter used in the remote I/O scan is the
1771ĆASB adapter.
Adapter
Adapter
Adapter BT Requests
Interrupt from Fault Routine.
Resident
·
¶
¶
¶
¶
per I/O Scan
¶
·
Logic
Scan