100k resistor on MS1 pin of A4988 Carrier Hello, I'm wondering why every circuit diagram (Of repRap electronics) has 100k resistor to ground on MS1 pin. I think this resistor is useless... Different pull-down resistor is on MS2 anyway... Thanks for answer :-). https://reprap.org/forum/read.php?13,347202,347202#msg-347202 Sat, 13 Jun 2026 01:41:05 -0400 Phorum 5.2.23 https://reprap.org/forum/read.php?13,347202,347924#msg-347924 Re: 100k resistor on MS1 pin of A4988 Carrier https://reprap.org/forum/read.php?13,347202,347924#msg-347924
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Traumflug
Early Pololu stepper drivers (A4983 based) didn't have such a pulldown onboard, so the big electronics board had to provide one. A4983 based ones are still in use and the pulldown doesn't conflict with newer ones, so it's still kept.

Gen7 electronics took a slightly different approach, fixing MS1 to high and saving a few parts at the loss of quarter and full step microstepping modes.

There was somethink before A4988? That is new for me :-).
I can see it now in [www.pololu.com]. Pulldown on MS1 is missing... Thx for answer :-).]]> FBITuco Controllers Wed, 30 Apr 2014 09:38:55 -0400 https://reprap.org/forum/read.php?13,347202,347881#msg-347881 Re: 100k resistor on MS1 pin of A4988 Carrier https://reprap.org/forum/read.php?13,347202,347881#msg-347881
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FBITuco
I'm wondering why every circuit diagram (Of repRap electronics) has 100k resistor to ground on MS1 pin.

Early Pololu stepper drivers (A4983 based) didn't have such a pulldown onboard, so the big electronics board had to provide one. A4983 based ones are still in use and the pulldown doesn't conflict with newer ones, so it's still kept.

Gen7 electronics took a slightly different approach, fixing MS1 to high and saving a few parts at the loss of quarter and full step microstepping modes.]]> Traumflug Controllers Wed, 30 Apr 2014 08:22:48 -0400 https://reprap.org/forum/read.php?13,347202,347725#msg-347725 Re: 100k resistor on MS1 pin of A4988 Carrier https://reprap.org/forum/read.php?13,347202,347725#msg-347725
Look at Sango scheme: [reprap.org]
There is additional external 100k pull-down resistor R3 on MS1 pin.

I know that internal resistors are there to pulling line down... It can't "fly" in the air. Try left unconnected input of ADC and You will see...

So... Why additional pull-down?]]> FBITuco Controllers Wed, 30 Apr 2014 01:27:17 -0400 https://reprap.org/forum/read.php?13,347202,347536#msg-347536 Re: 100k resistor on MS1 pin of A4988 Carrier https://reprap.org/forum/read.php?13,347202,347536#msg-347536 A4988 Data Sheet:
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Microstep Select (MSx). The microstep resolution is set by
the voltage on logic inputs MSx, as shown in table 1. The MS1 and
MS3 pins have a 100 kΩ pull-down resistance, and the MS2 pin
has a 50 kΩ pull-down resistance.

As to being useless, I'd have to defer to the electrical engineers at Allegro in their design decision on why MS1 and MS3 need a 100k pull down resistor and MS2 needs a 50k one. But based on their design decision, my guess is it IS useful and that those resistors are just pulling the line low to ensure they are low unless the jumpers are enabled to set them high.]]> cdru Controllers Tue, 29 Apr 2014 16:25:02 -0400 https://reprap.org/forum/read.php?13,347202,347202#msg-347202 100k resistor on MS1 pin of A4988 Carrier https://reprap.org/forum/read.php?13,347202,347202#msg-347202
I'm wondering why every circuit diagram (Of repRap electronics) has 100k resistor to ground on MS1 pin. I think this resistor is useless... Different pull-down resistor is on MS2 anyway...

Thanks for answer :-).]]> FBITuco Controllers Tue, 29 Apr 2014 08:13:52 -0400