Rockwell Automation 1785-LTx,D17856.2.1 Classic PLC-5 Programmable Controllers Users Manual - Manual (Page 117)

Transferring Discrete and BlockĆTransfer Data
Chapter 8
8-22
Considerations for ProcessorĆResident Local Racks
The following are programming considerations when you are block-
transferring data in a processor-resident local rack.
Within the processor-resident local rack, limit the number of
continuous-read block transfers to 16 transfers of 4 words each or 8
transfers of 64 words each. If you attempt to exceed this block-transfer
limit, a checksum error (error code -5) occurs.
Block-transfer instructions to any of the following modules residing in
the processor-resident local rack result in frequent checksum errors.
- 1771-OFE1, -OFE2, and -OFE3 modules, all versions prior to series
B, revision B.
- 2803-VIM module, all versions prior to series B, revision A
- IMC-120, all versions
To eliminate the checksum errors, replace your modules with the current
series and revision. If replacement is not possible then:
1. Using 6200 Series PLC-5 Programming Software release 4.11/4.12
or later, go to the Processor Status screen.
2. With the processor in PROG mode, set user control bit 4 to
1. The
User Control Bit word is S:26.
3. Change the processor mode from PROG to RUN.
Do not program IIN or IOT instructions to a module in the same
physical module group as a BT module unless you know a block
transfer is not in progress. If you must do this, then use an XIO
instruction to examine the EN bit of the block-transfer instruction to
condition the IIN and IOT.