Rockwell Automation 1785-BCM_BEM, D17856.5.4 PLC-5 Backup Communication Module User Manual - Manual (Page 153)

Reference Information
Appendix B
B-6
Table B.B
Data Table Typical Transfer Time Using Method 2 Program
with Minimal Progam Scan (4–9 ms)
Number of Blocks
Being Transferred Number of Words
Being Transferred
Transfer Time (in ms)
for Series A BCM
(see notes 1 & 2) Transfer Time (in ms)
for Series B BCM
Fast Transfer Mode
Enabled (see notes 1,
3, & 4)
1 62 170–250 60–80
3 186 200–300 90–120
7 434 350–500 130–180
10 620 350–600 170–230
16 992 400–1000 180–260 5
32 1984 – 320–720 6
64 3968 – 700–1400 7
1 These times do not significantly change with program scan, but as the number of blocks increase
so does program scan.
2 Times were taken using a PLC-5/25 processor.
3 Series B BCM module with fast mode disabled is approximately 50% slower than the times
shown.
4 Times were taken using a PLC-5/40 processor with one channel configured for DH+ and three
channels configured for remote I/O scanner at 230 kbaud.
5 Program scan 12–16 ms.
6 Program scan 20–25 ms.
7 Program scan 30–35 ms.
General Considerations
Data table transfer time increases with the number of blocks in a data
segment. This is because the secondary 1785-BCM module must wait for
the last block to be transferred from the primary system before it can
release its first block for BTR by the secondary processor (normal
transfer).
In time-critical applications, you may use Fast Data Transfer mode (switch
2 of switch assembly SW1). In this case, the secondary processor does not
need to wait for the complete data segment in order to release its first block
for BTR by the secondary processor.