PMAC Quick Reference Guide Single Character I/O Bringing in a single character from, or sending out a single character to, the serial port or host port (PC or STD) is the highest priority in PMAC. This task takes only 200 nsec per character, but having it at this high priority ensures that the host cannot outrun PMAC on a character-by-character basis. This task is never a significant portion of PMAC’s total calculation time. Note that this task does not include processing a full command; that happens at a lower priority (see the Background Tasks section). Commutation Update The commutation (phasing) update is the second highest priority on PMAC.
In a 20 MHz PMAC, this task takes 3 µ sec per update cycle for each motor commutated by PMAC (Ix01=1). The master clock frequency and jumpers E98, E29-E33, determines the frequency of this task. The default update frequency is 9 kHz (110 µ sec cycle). At the default, the commutation of each motor takes approximately 3% of PMAC’s computational power. Servo Update The servo update – computing the new commanded position, reading the new actual position, and computing a command output based on the difference between the two – is the third highest priority on PMAC.
In a 20 MHz PMAC, this task takes 30 µ sec per update cycle for each activated motor (Ix00=1) plus about 30 µ sec for general servo tasks such as the encoder conversion table. The master clock frequency and jumpers E98, E29-E33, E3-E6 determine the frequency of this task. The default update frequency is 2.26 kHz (442 µ sec cycle). At the default, the servo update of each motor takes approximately 7% of PMAC’s computational power. 8 Introduction