Rockwell Automation 1785-Vx0B, D17856.5.9 PLC-5 VME VMEbus Programmable Controllers User Manual - Manual (Page 122)

Performance and Theory of Operations
Chapter 7
7-17
In this example,
R = 1 because the value of D (6 ms) < 15 ms logic scan time
block-transfer duration (ms) = 6 x 1 or 6 ms
The block-transfer duration shown above does not affect logic scan time.
This transfer of data occurs concurrent with execution of program logic.
Remote 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 7.4 shows timing loops for block transfer from a PLC-5/VME
processor.
Figure 7.4
Transferring Block Data to Local and Remote I/O
Rack 7
Remote I/O
Scan
Remote I/O
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
BT Requests
Q
A
Q = Queue
A = Active
Buffer
Q
A
One transfer per
I/O scan
BTR or BTW Data
❶
The adapter used in the remote I/O scan is the
1771-ASB adapter.
Adapter
Adapter
Adapter BT Requests
Interrupt from STI or Fault Routine
❷
❶
❶
❶
❶
❷
Logic
Scan
Program Scan