Reference Manual

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PMAC 2 Software Reference

PMAC I-Variable Specification 147

3: ......................x4 quadrature decode CW

4: ......................Pulse and direction CCW

5: ......................x1 quadrature decode CCW

6: ......................x2 quadrature decode CCW

7: ......................x4 quadrature decode CCW

8: ......................Internal pulse and direction

9-11: .................Not used

12: ....................MLDT pulse timer control

13-15: ...............Not used

In any of the quadrature decode modes, PMAC2 is expecting two input waveforms on

HWA1 and HWB1, each with approximately 50% duty cycle, and approximately one-

quarter of a cycle out of phase with each other. “Times-one” (x1) decode provides one

count per cycle; x2 provides two counts per cycle; and x4 provides four counts per cycle.

The vast majority of users select x4 decode to get maximum resolution.

The “clockwise” (CW) and “counterclockwise” (CCW) options simply control which

direction counts up. If you get the wrong direction sense, simply change to the other

option (e.g. from 7 to 3 or vice versa)

Note:

Changing the direction sense of the decode for the feedback encoder

of a motor that is operating properly will result in unstable positive

feedback and a dangerous runaway condition in the absence of other

changes. The output polarity must be changed as well to re-

establish polarity match for stable negative feedback.

In the pulse-and-direction decode modes, PMAC2 is expecting the pulse train on HWA1,

and the direction (sign) signal on HWB1. If the signal is unidirectional, the HWB1 line

can be allowed to pull up to a high state, or it can be hardwired to a high or low state.

If I990 is set to 8, the decoder inputs the pulse and direction signal generated by Channel

1*’s pulse frequency modulator (PFM) output circuitry. This permits the PMAC2 to create

a phantom closed loop when driving an open-loop stepper system. No jumpers or cables

are needed to do this; the connection is entirely within the ASIC. The counter polarity

automatically matches the PFM output polarity. This mode is only supported on “B” and

newer revisions of the DSPGATE2 IC.

If I990 is set to 12, the timer circuitry is set up to read magnetostrictive linear displacement

transducers (MLDTs) such as Temposonics

. In this mode, the timer is cleared when the

PFM circuitry sends out the excitation pulse to the sensor on PULSEn, and it is latched

into the memory-mapped register when the excitation pulse is received on HWA1. This

mode is only supported on “B” and newer revisions of the DSPGATE2 IC.