Allegro 4983 - Low Current Microstepping

This a subject related to the Nophead's great blog; specifically about low current microstepping and the allegro chips. As I believe Nophead notes, the A4988 datasheet speaks about tying the OSC pin to ground to achieve a constant 30 us delay.

The A4983 datasheet does not mention this, but seems to give the same delay formula.

Also, everything I can seem to find that describes the differences between the A4983 and the newer A4988 only note over current protection and the addition of a pull down on the MS1 pin.

Thus, the question: does the A4983 *also* go into this constant delay mode when the OSC is grounded i.e. this "feature" was just not mentioned in the datasheet or is this behavior another, albeit undocumented difference between the two chips?

Thanks in advance.

After posting this message, I went back and reread both data sheets and the fog is starting to lift. Basically, the question I posed in my first posting is ill formed it that the real issue is the "automatic mixed delay" vs. the "always mixed delay". Bottom line, the two chips are different in that regard with the newer a4988 implementing the "ground ROSC" to get always mixed delay. Sorry for the churn.

mars bonfire Wrote:
-------------------------------------------------------
> This a subject related to the Nophead's great
> blog; specifically about low current microstepping
> and the allegro chips. As I believe Nophead
> notes, the A4988 datasheet speaks about tying the
> OSC pin to ground to achieve a constant 30 us
> delay.
>
> The A4983 datasheet does not mention this, but
> seems to give the same delay formula.
>
> Also, everything I can seem to find that describes
> the differences between the A4983 and the newer
> A4988 only note over current protection and the
> addition of a pull down on the MS1 pin.
>
> Thus, the question: does the A4983 *also* go into
> this constant delay mode when the OSC is grounded
> i.e. this "feature" was just not mentioned in the
> datasheet or is this behavior another, albeit
> undocumented difference between the two chips?
>
> Thanks in advance.

So what to do with my A4983 ? Put ROSC to vcc 5 volt? (to set max off time to 30us)

From my blog:

Quote

What to do with my A4983 Pololus? Well if I increase the current to 1.3A and change the resistor to 36K then the minimum frequency is 17kHz, which is ultrasonic to me nowadays due to the age of my ears. Alternatively switching to 8× microstepping and using a 22K resistor keeps it above 30kHz and the current can be 1A.

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[www.hydraraptor.blogspot.com]

nophead Is it R4 or what resistor do you mean?

Yes R4, the resistor on the ROSC pin to ground.

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[www.hydraraptor.blogspot.com]