Bradley Smoker PLC-5 For Controller-Resident Local Racks, 20Communicating with Remote I/O

6-20Communicating with Remote I/O

•When performing block-transfers (controller-resident local or remote I/O) in any PLC-5 controller, clear the output image table corresponding to the block-transfer module rack location before changing to run mode. If you do not clear the output image table, then you encounter block-transfer errors because unsolicited block-transfers are being sent to the block-transfer module (i.e., if a block-transfer module is installed in rack 2, group 4, clear output word O:024 to 0; do not use the word for storing data).

•If you use remote block-transfer instructions and have the timeout bit (.TO) set to 1, then the controller disables the 4-second timer and continues to request the block-transfer for 0-1 seconds before setting the error (.ER) bit.

•A PLC-5 controller with at least one channel configured as an adapter could incur a non-recoverable fault when you switch it from run to program mode.

To avoid this possibility, program the scanner to request only two or three block-transfers from the PLC-5 adapter at one time by conditioning the block-transfer instructions with the done/error bits.

For Controller-Resident Local Racks

The following are programming considerations when you are block-transferring data in a controller-resident local rack.

•Within the controller-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 controller-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:

1.Go to the controller configuration screen in your programming software.

2.With the controller in program mode, set user control bit 4 (S:26/4) to 1 (the local block-transfer compatibility bit).

3.Change the controller mode from program to run.

Publication 1785-UM012D-EN-P - July 2005