PMAC Quick Reference Guide VME Mailbox Processing Reading or writing a block of up to sixteen characters through the VME mailbox registers is the fourth highest priority in PMAC. The host controls the rate at which this happens. This never takes a significant portion of PMAC’s computational power. Real-Time Interrupt Tasks The real-time interrupt (RTI) tasks are the fifth highest priority on PMAC. They occur immediate after the servo update tasks at a rate controlled by parameter I8 (every I8+1 servo update cycles). There are two significant tasks occurring at this priority level: PLC 0 / PLCC0 and motion program move planning. All C.S. programs checked? Yes I5=1 or I5=3?
Yes Enabled PLC0 Enabled PLCC0 No No decrement the watchdog register by 8 PMAC will scan the lines of each program running in the different coordinate systems and will calculate the necessary number of move commands. C.S. program running? Yes End of Interrupt The number of move commands of pre-calculation can either be zero, one or two and depending on the type of motion commands and the mode in which the program is being executed. No Next coordinate system No move calculations needed? Yes Non-move commands are executed immediately as they are found. The scan of any given motion program will stop as the necessary number of moves is calculated.
It resumes when previous move commands are completed and more move-planning calculations are required. Read next line of the motion program line contains move commands? In the execution of a motion program, if PMAC finds two jumps backward (toward the top) in the program while looking for the next move command, PMAC will pause execution of the program and not try to blend the moves together. It will go on to other tasks and resume execution of the motion program on a later scan. Two statements can cause such a jump back: ENDWHILE and GOTO ( RETURN does not count). Yes No calculate move execute line Yes No end of program?
Background Tasks In the time not taken by any of the higher-priority tasks, PMAC will be executing background tasks. There are three basic background tasks: command processing, PLC programs 1-31, and housekeeping. The frequency of these background tasks is controlled by the computational load on PMAC: the more high- priority tasks are executed, the slower the background tasks will cycle through; and the more background tasks there are, the slower they will cycle through. Each PLC program executes one scan (to the end or to an ENDWHILE statement) uninterrupted by any other background task (although it can be interrupted by higher priority tasks).
In between each PLC program, PMAC will do its general housekeeping, and respond to a host command, if any. Introduction 9 Execute next I5=2 or I5=3? Yes enabled PLC Execute first No enabled PLCC perform safety checks: end of travel limits Execute next amplifier faults enabled PLCC following error sets watchdog register to 4095 All PLCCs Yes No checked? command response (communications) command response (communications)