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Modulating stepper speed with ACC-24E2S over MACRO
We have the following physical setup:

PowerPMAC CPU in UMAC chassis
MACRO fiber link
Stepper drive

With this configuration, and the default ms0, mi903 of 2258, we cannot modulate the stepper speed very well. As we increase the open loop output (#1 out <n>), the motor jumps from stopped to rotating at a speed equivalent to a step output frequency of 150 steps/second. This occurs when the output magnitude reaches 1. It appears that with this configuration, the stepper speed is limited to discrete values. The next step is a motor speed of around 300 steps/second.

Changing ms0, mi903 to 2298 (increasing PFM clock divider from 2 to 7) reduces the lowest achievable speed, and reduces the increments for each speed change.

The ACC-5E3 manual states that only the high 16 bits of Gate3[i].MacroOutA[j][2] are transferred across the MACRO link.

Is there a configuration change we can make on the ACC-24E2S other than the PFM clock divider, to allow better speed modulation? What I would like is for the stepper speed to respond correctly to fractional changes in the motor output command.
I think the following "outline" would be the best approach:
1. Enable MLDT mode MI161 – 168, writes to C register once at power on and disable write to C register.
2. Use MI19 = 0 (xfer phase rate). It’s done in background and not phase interrupt but should be fast enough.
3. MI20 (MI21-68 xfer enable) &
4. MI21 – 68 (24 bit xfer format) There’s an X or Y 24 bit transfer FROM and TO format

See the "old" MACRO SRM for details on these:

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