Rockwell Automation 1785-Lxxx Enhanced and Ethernet PLC-5 Programmable Controllers - Manual (Page 268)

Publication 1785-UM012D-EN-P - July 2005
18-6 Using Processor Input Interrupts
Monitoring Controller
Input Interrupts Use the controller status screen in your programming software to monitor
PIIs.
Use S:51/0-15 within the PII file because these bits are:
• mapped from the actual input module being used for the PII
• retentive
For the PII routine to execute properly, do not use the addresses of the input
module’s bits within the PII routine.
This PII Field Stores
Status File
Address
Events since last
interrupt Displays the number of PII events (the input conditions that caused the interrupt)
since the last interrupt. S:52
PII changed bits Displays the bit transitions that caused the interrupt. You can use this information
to condition other rungs in your ladder program.
If one of these bits is already set (i.e., a previous interrupt set the bit), the controller
sets a minor fault (S:10/2) to indicate a possible PII overlap. If you want to monitor
this overlap, make sure the last rung in your PII program clears this return mask in
the status file.
S:51
Last scan time Displays the current or last scan time through the PII. S:55
Max observed scan
time Displays the maximum value that was displayed in the last
scan field. S:56
Word not in local
rack This box is checked if the input word number specified is not on the local rack or if
there is not an input module in the slot addressed. S:10/11
No command blocks This box is checked if no command blocks exist to get the PII. You can use the
controller’s internal counter or bit transition to execute the PII.
S:10/13
User routine overlap This box is checked if a set condition exists in the PII return mask or changed bits
(possibly set by a previous interrupt) before completing the currently executing PII
routine. PII changed bits are retentive. It may be necessary to place a MOV
instruction on the last rung in the PII file. Move 0 in S:51 to reset the PII bits before
finishing the PII file. If this is not done, a PII overlap bit will be set on that status
page, causing this minor fault.
S:10/12