User`s manual

1.0 - Introduction to PMAC

Page - 8

1.6.1 - 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

background tasks below).

Input buffer

E N A P L C 1

I 3 = 0

Output buffer

1.6.2 - Commutation Update

The commutation (phasing) update is the second highest priority on PMAC. In a 20 MHz PMAC this task takes 3 µsec 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 µsec cycle). At the default, the

commutation of each motor takes approximately 3% of PMAC's computational power.

1.6.3 - 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 µsec per update cycle for each activated motor (Ix00=1) plus about 30 µsec for general servo tasks such as the

encoder conversion table. The frequency of this task is determined by the master clock frequency, and jumpers E98, E29-

E33, E3-E6. The default update frequency is 2.26 kHz (442 µsec cycle). At the default, the servo update of each motor

takes approximately 7% of PMAC's computational power.

1.6.4 -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.

Amplifier

AGnd

DAC

Commanded

Position

ctual

Position

PID

Serial or Bus

connection

Amplifier

AGnd

DAC 1

DAC 2

Encoder

Commutation

Algorithm