Rockwell Automation 1785-BCM_BEM, D17856.5.4 PLC-5 Backup Communication Module User Manual - Manual (Page 94)

Switchover Considerations
Chapter 6
6-9
Several of the data table sections in the PLC-5 processor are not structured
with single 16-bit words. You need to consider this when applying the
1785-BCM module.
For example, the BTW of the primary processor transfers 62 words of data
to the secondary processor (plus the packet length and block ID word).
Some structures such as timers, counters, and floating point control files
have three words. If all related words don’t fit in a block, some words may
be truncated, creating a partial structure in the secondary processor
(Figure 6.2).
Figure 6.2
Partial Structure in BTW
BTW (64 words)
To secondary
Packet Length
Block ID
Words 3 – 62
.
.
.
Word 1
Word 2
Accumulated value is truncated
Word 63
Word 64 Preset value Counter
Control Word
Word 65
11107I
Problem structures include:
timer values
counter values
floating point elements
control
registers
Data Table Considerations