Rockwell Automation 1785 PLC-5 User Manual download pdf (Page 266)

Publication 1785-UM012D-EN-P - July 2005

18-4 Using Processor Input Interrupts

PII configuration changes are not put into effect until the controller goes from

program to run or test mode.

Design Considerations

Consider the following guidelines when planning PIIs.

• Do not use 2-slot addressing when using PIIs.

• Do not use 1771-IG or -IGD, 8- and 16-point TTL modules for the PII.

Use the 1771-IQ16 input module instead. Since the module’s input

delay filter is selectable, you can set the delay to 0 or about 200 ms.

• Avoid using a block-transfer module in the controller-resident rack with

a PII configured because you could miss an input pulse while a

block-transfer of data is in progress. However, if you need to use

block-transfers, make sure that a PII input pulse is at least 400 ms, which

causes the block-transfer not to affect the PII.

• Online editing affects the performance of a PII routine. A PII cannot

interrupt the controller while it is managing its memory due to the

online edits being made. The PII input must be on for an amount of

time slightly greater than the actual time required to complete the online

edits. If not, the PII does not execute.

• Clear S:51 in one of two ways:

– using a CLR instruction (see ²)

– placing a MOV (move) instruction on the last rung in the PII file.

Move a 0 into S:51 to reset the PII bits before finishing the PII file.

IMPORTANT

When the controller runs an PII with a block-transfer

instruction to a remote chassis, the MCP resumes

processing while waiting for the block-transfer to complete

unless a UIE/UID instruction pair is used.

IMPORTANT

If S:51 is not cleared, a PII overlap bit is set on that status

page, causing a minor fault.

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Rockwell Automation 1785 PLC-5 User Manual Page 266