Reference Manual

PMAC 2 Software Reference
PMAC I-Variable Specification 145
machine interface channel n. If a three-phase direct PWM command format is desired,
I9n6 should be set to 0. If signal outputs for (external) digital-to-analog converters are
desired, I9n6 should be set to 1 or 3. In this case, the C output can be used as a
supplemental (non-servo) output in either PWM or PFM form. For example, it can be used
to excite an MLDT sensor (e.g. Temposonics
TM
) in PFM form.
I9n7 Output n Invert Control {PMAC2 only}
Range
0 .. 3
Units
none
Default
0
Remarks
I9n7 controls the high/low polarity of the command output signals for Channel n. The
default non-inverted outputs are high true.
For PWM signals on Outputs A, B, and C, this means that the transistor-on signal is high.
Delta Tau PWM-input amplifiers, and most other PWM-input amplifiers, expect this non-
inverted output format. For such a 3-phase motor drive, I9n7 should be set to 0.
Note:
If the high/low polarity of the PWM signals is wrong for a
particular amplifier, what was intended to be deadtime between top
and bottom on-states as set by I904 and I908 becomes overlap. If
the amplifier input circuitry does not lock this out properly, this
causes an effective momentary short circuit between bus power and
ground. This would destroy the power transistors very quickly.
For PFM signals on Output C, non-inverted means that the pulse-on signal is high
(direction polarity is controlled by I9n8). During a change of direction, the direction bit
will change synchronously with the leading edge of the pulse, which in the non-inverted
form is the rising edge.
If the drive requires a set-up time on the direction line before the rising edge of the pulse,
the pulse output can be inverted so that the rising edge is the trailing edge, and the pulse
width (established by I904 or I908) is the set-up time.
For DAC signals on Outputs A and B, non-inverted means that a 1 value to the DAC is
high. DACs used on Delta Tau accessory boards, as well as all other known DACs always
expect non-inverted inputs, so I9n7 should always be set to 0 or 2 when using DACs on
Channel n.
Note:
Changing the high/low polarity of the digital data to the DACs has
the effect of inverting the voltage sense of the DACs’ analog
outputs. This changes the polarity match between output and
feedback. If the feedback loop had been stable with negative
feedback, this change would create destabilizing positive feedback,
resulting in a dangerous runaway condition that would only be
stopped when the motor exceeded Ix11 fatal following error.
I9n8 Output n PFM Direction Signal Invert Control {PMAC2 only}
Range
0 .. 1
Units
none
Default
0
Remarks
0 = Do not invert direction signal (+ = low; - = high)