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Acc-24M2A Using PFM


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I'm trying to drive a stepper motor with encoder on an ACC-24M2A by MACRO ring.


I work on a UMAC rack with a Power PMAC CPU and an ACC-5E3 card.


The communication by MACRO works. I can see the encoder feedback in the IDE.


I have added the jumpers E5 and E6 to generate PFM signal on J11 & J12 connectors (Pinout : Pulse+ 9 / Pulse- 22 / Dir+ 8 / Dir- 21).


Motor[9].pDac = Acc5E3[1].MacroOutA[0][2] // PWMC to drive in PFM


The Pulse signal seems be wrong. It's a TTL signal but it's to the high level during 95% of the time. It's as if there was an inversion between low and high levels.


The PFM_CLK is at 305.72 kHz (M993 = 2298).


I have checked the *.PwmDeadTime (MI994) of the acc-24M2A, but it seems be ok (=15, so PFM Pulse width = 49 us).


To conclude, the Driver can't detect the edges.


Anybody have any idea? I can give more details.


Thanks for your help,



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Are you sure? For now, I have a TTL signal 0 - +5 Volts.


There is just something strange concerning the duty rate.


If I make an inversion as you say, I will have a negative signal 0 - -5 Volts.




Raphael Millet

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The pulse and direction output on most of Delta Tau products are driven by CMOS differential line drivers which meet the standard RS-422 requirements. This means that each line (non-inverting and inverting) are both in CMOS levels. Both inverting and non-inverting signals are always between 0 to 5V. The line driver used on ACC-24M2A in particular has the following thresholds for low and high signals:


Vout - High : Min 2.5V

Vout - Low: Max 0.5V


The line receiver on the stepper drive combines these complementary signals through a differential line receiver and reconstructs the original pulse and direction signals. Please see the following diagram showing the signal levels compared to the input signal.




For further information on this line driver, please check the documentation for ST34C87 QUAD RS-422 CMOS Differential Line Driver.

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