Delta Tau PMAC2 PCI User Manual download pdf (Page 43)

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PMAC2 User Manual

Setting Up PMAC2 for Sine-Wave Output Control 35

Hardware Clock Frequency Control: I903, I907

I903 determines the frequency of four hardware clock signals use for machine interface channels 1-4;

I907 does the same for machine interface channels 5-8. These can probably be left at the default values.

The four hardware clock signals are SCLK (encoder sample clock), PFM_CLK (pulse frequency

modulator clock, DAC_CLK (digital-to-analog converter clock), and ADC_CLK (analog-to-digital

converter clock).

Only the DAC_CLK signal is directly used with the sine-wave output, to control the frequency of the

serial data stream to the DACs. The default DAC clock frequency of 4.9152 MHz is suitable for the

DACs on the recommended Acc-8E analog interface board. Refer to the I903 and I908 descriptions for

detailed information on setting these variables.

The encoder SCLK frequency should be at least 20% greater than the maximum count (edge) rate that is

possible for the encoder on any axis. Higher SCLK frequencies than this minimum may be used, but

these make the digital delay anti-noise filter less effective.

DAC Strobe Control: I905, I909

PMAC2 generates a common DAC strobe word for each set of 4 machine interface channels. It does this

by shifting out a 24-bit word each phase cycle, one bit per DAC clock cycle, most significant bit first.

I905 contains this word for Channels 1-4; I909 contains this word for Channels 5-8. The default values of

$7FFFC0 are suitable for use with the DACs on the recommended Acc-8E analog interface board.

Parameters to Set Up Per-Channel Hardware Signals

For each machine interface channel n (n = 1 to 8) used for sine wave analog outputs, a few I-variables

must be set up properly.

Encoder Decode Control: I9n0

I9n0 must be set up to decode the commutation encoder properly. Almost always a value of 3 or 7 is used

to provide times-4 decode of a quadrature encoder (4 counts per encoder line). The difference between 3

and 7 is the direction sense of the encoder; set this variable so the motor counts up in the direction wanted.

The polarity sense of the Ix72 commutation phase angle parameter must match that of I9n0 for the

particular wiring; if it is wrong, it will lock into a position rather than generate continuous torque. A test

for determining this polarity match is given below. Remember that if I9n0 is changed on a working

motor, also change Ix72.

Output Mode Control: I9n6

I9n6 must be set to 1 or 3 to specify that outputs A and B for Channel n are in DAC mode, not PWM. A

setting of 1 puts output C (not used for servo or commutation tasks in this mode) in PWM mode; a setting

of 3 puts output C in PFM mode.

Output Inversion Control: I9n7

I9n7 controls whether the serial data streams to the DACs on Channel n are inverted or not. The default

value of 0 (non-inverted) is suitable for use with the recommended Acc-8E analog interface board.

Inverting the bits of the serial data stream has the effect of negating the DAC voltage. In a commutation

algorithm this is equivalent to a 180

phase shift, which would produce runaway if the system were

working properly before the inversion.

Parameters to Set Up Motor Operation

Several I-variables must be set up for each Motor x to enable and configure the sine-wave output for that

motor. Of course, Ix00 must be set to 1 for any active motor, regardless of the output mode for that

motor.

Commutation Enable: Ix01

Ix01 is set to 1 to activate the commutation algorithms for Motor x.

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Delta Tau PMAC2 PCI User Manual Page 43

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