User`s manual

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1.0 - Introduction to PMAC

Page - 9

1.6.5 - 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.

PMAC will scan the lines of each program running in the

different coordinate systems and will calculate the necessary

number of move commands.

The number of move commands of precalculation could be

either zero, one or two and it depends on the type of motion

commands and the mode in which the program is being

executed.

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.

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).

1.6.6 - 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.

All enabled PLCC programs execute one scan (to the end or to an ENDWHILE statement) starting from lowest numbered

to highest uninterrupted by any other background task (although it can be interrupted by higher priority tasks). At power-

on\reset PLCC programs run after the first PLC program runs.

The receipt of a control character from any port is a signal to PMAC that it must respond to a command. The most common

control character is the carriage return (<CR>), which tells PMAC to treat all the preceding alphanumeric characters as a

command line. Other control characters have their own meanings, independent of any alphanumeric characters received.

Here PMAC will take the appropriate action to the command, or if it is an illegal command, it will report an error to the

host.

Between each scan through each background PLC program, PMAC performs its housekeeping duties to keep itself properly

updated. The most important of these are the safety limit checks (following error, overtravel limit, fault, watchdog, etc.)

Although this happens at a low priority, a minimum frequency is ensured because the watchdog timer will trip, shutting

down the card, if this frequency gets too low.

Enabled

PLC0

Enabled

PLCC0

move

calculations

needed?