Reference Manual

PMAC 2 Software Reference

PMAC I-Variable Specification 85

Mode 1: When PMAC is not commutating Motor x (Ix01 = 0), Ix29 serves as the offset

for the single command output value, usually a DAC command. Ix29 is added to the

output command value before it is written to the command output register.

Mode 2: When PMAC (PMAC(1) only) is not commutating Motor x (Ix01 = 0) but is in

sign-and-magnitude output mode (Ix02 bit 16 = 1), Ix29 is the offset of the command

output value before the absolute value is taken (Ix79 is the offset after the absolute value is

taken). Ix29 is typically left at zero in this mode, because it cannot compensate for real

circuitry offsets.

Mode 3: When PMAC is commutating Motor x (Ix01 Bit 0 = 1) but not closing the current

loop (Ix82 = 0), Ix29 serves as the offset for the first of two phase command output values

(Phase A), for the address specified by Ix02; Ix79 serves the same purpose for the second

phase (Phase B). Ix29 is added to the output command value before it is written to the

command output register.

When commutating from a PMAC(1), Phase A is output on the higher-numbered of the

two DACs (e.g. DAC2), Phase B on the lower-numbered (e.g. DAC1). When

commutating from a PMAC2, Phase A is output on the A-channel DAC (e.g. DAC1A),

Phase B on the B-channel DAC (e.g. DAC1B).

As an output command offset, Ix29 is always in units of a 16-bit register, even if the actual

output device is of a different resolution. For example, if a value of 60 had to be written

into an 18-bit DAC to create a true zero command, this would be equivalent to a value of

60/4=15 in a 16-bit DAC, so Ix29 would be set to 15 to cancel the offset.

Mode 4: When PMAC (PMAC2 only) is commutating (Ix01 Bit 0 = 1) and closing the

current loop for Motor x (Ix82 > 0), Ix29 serves as an offset that is added to the phase

current reading from the ADC for the first phase (Phase A), at the address specified by

Ix82 minus 1. Ix79 performs the same function for the second phase. The sum of the

ADC reading and Ix29 is used in the digital current loop algorithms.

As an input feedback offset, Ix29 is always in units of a 16-bit ADC, even if the actual

ADC is of a different resolution. For example, if a 12-bit ADC reported a value of -5

when no current was flowing in the phase, this would be equivalent to a value of -5*16=-

80 in a 16-bit ADC, so Ix29 would be set to 80 to compensate for this offset.