Slow communications - Delta Tau - #1

PLCs and PLCCs at

lalchdog timer failures.

Any SEND, COMMAND, or DISPLAY action statement should be dono only on an edge-triggered condition because the PLC can cycle faster than ¡hese operations can process their information and the communications channels can gel overwhelmed if these statements get executed O; through the PLC.

IF (Mil—1]

IF (Pll-0)

COMMAND"#1J+" Pll=l

ENDIF

ELSE

Pll-0

ENDIF

Usually, PMAC will have enough speed and calculati without the user having to worry. Some applications

make PMAC' run more e flic ie nil) some priority level optimization -mould lie done. When I'M AC' begins to run out of lime, problems such as sluggish community lions, slow PLC/PLC C scan rales, run­time errors, and even tripping the Watchdog timer can occur.

• The active part of the Lmcoder Conversion fable is ended by the llrsl Y word that is all zeros. For an implication nilh less than eight encoders (the default lahlc converts the eight incremental encoder registers on the hase PMAC). a lasl entry with all zeros in the Y word could he defined as necessary.

• Check to see if everything per formed in the Real Time Interrupt ( RTI) is necessary or if some of it could be moved to a lower priority or slowed down. Pl.CO could be done as PLCCI, or the RTI could be done every fourth or lil'th servo cycle selling IX 3 or higher.

• Large PLC programs can be split into a lew shorter I'l C programs. This increases the frequency of Housekeeping and communications bv giv tng more breaks in PLC scans.

■ Motion program WHILE {condition)WAIT statement con hi he done as follow s: WHILE(condi tion) DWELL20 ENDWHILE

This will give more time to other RTI jobs such as Move Planning and PLC/PLCCO.

• If the routines of lower priority than the servo loop are not executing last enough, consider slowing down the servo update rale (increasing ihe update lime). Il may be updating lasler than is required for the dynamic performance needed. If so. processor lime is being wasted on needless extra updates. For example, doubling the sen o update lime from 442 msec to 885 msec virtually doubles the time available for motion and I'l C program c\eeuliou. allowing much faster motion block rales and PLC

A faster than 20 Ml Iz PMAC will perform calculations taster, in proportion to the corresponding

clock rate increase. In general, a clock rate computational time available. These cases ; involved (small-moves contouring), maintai control performance.

desirable lo ioti-cast the lì TI share ofthe total nclude application ubere large movecalculationsare ning the sanie servo-loop rate and Iherefore the same