[carl benz]

i have some a3955 chips and i want to use them in a microstepping based driver using pic16f628a ,any ideas ,pleeeeeeeeez post

[doorknob]

I have not worked with a 16F628A for about 8 years, so my memory is a bit fuzzy, and I have no experience using the A3955 , however a quick look at the A3955 datasheet tells me that it should be "do-able".

You will need two of the chips to drive a single bipolar stepper motor. You will also need to implement a look-up table to convert step and direction signals into the proper digital outputs to send to the driver chip, but you should have enough I/O pins on the 16F628A to do it.

See "Fig. 4 - typical application" in the A3955 datasheet for how to hook it up, and the "Table 4 - step sequencing" figure on the next page to see how to send the signals to the driver depending on which microstepping factor you want to use. For preliminary development work you might want to start out with single-stepping (since it is the least complicated pattern) and then when you have that working, try expanding the operation to microstepping.

[carl benz]

look to the pic16c621 datasheet there was a schematic posted by microchip on how to driver 2 a3955 with preprogramed pic16c621, it can help a little in finding a solution, plz reply

[doorknob]

I did not find the A3955 info in the PIC16C621 datasheet.

Can you be more specific about where that info is located in the datasheet as well as what your specific questions are about how to use the A3955 with a PIC?

[arvidj]

I think doorknob indicated it was the A3955 data sheet ...

... See "Fig. 4 - typical application" in the A3955 datasheet for how to hook it up, and the "Table 4 - step sequencing" figure on the next page to see how to send the signals to the driver depending on which microstepping factor you want to use. ...

[carl benz]

you asked me to be more specific; i want to remove pic16c621 from the shematic and replace it with 16f628a, by the way here is the datasheet

[doorknob]

Thanks for the clarification - I was looking at the regular PIC16C621 datasheet, and I had not located the datasheet that you posted for the custom pre-programmed version of the PIC16C621.

My guess is that they used the 74HC595 because the 16C621 does not have enough digital I/O pins to control two A3955s directly.

So I think that to use a 16F628A in that schematic in place of the 16C621 you would want to eliminate the 74HC595, and instead connect the wires that previously went to the 74HC595 output pins to available digital I/O pins of the 16F628A (and ignore the connections from the 16C621 that go to the 74HC595 input pins).

My interpretation of how they are using the 74HC595 is that it sends the D0, D1, and D2 signals (identified in Table 4 of the A3955 datasheet) that generate the corresponding microstep pattern (along with the Phase signals, which come directly from the 16C621).

Unfortunately, since the 16C621 firmware is proprietary and not disclosed, you will have to infer how it works (from the Microchip description and from the details in the A3955 datasheet).

[carl benz]

what about driving them with alan's picstep, is that possible ???? any schematics??

[doorknob]

I have no experience with the picstep controller.

After doing some quick searching, it looks like it is possible that the picstep uses LMD18245 H-bridge chips and a PIC16F628. While I have no experience with the LMD18245 either, if that is the case, then it looks like the LMD18245 may use a DAC input for controlling the microstepping similarly to the A3955 (although with 4 inputs instead of 3), which would lead me to conclude that you might be able to use the picstep firmware and schematic as a guide. However it would be necessary for you to examine it in detail to be certain - it is possible that I have not correctly interpreted the function of the DAC inputs in the overall operation of the driver.

[H500]

The picstep code is 90% compatible, but you will need to modify the step table. Otherwise, the motor will run very roughly.

[carl benz]

any schematics???? any *.hex???

[H500]

Picstepper is open source. I believe everything is in his thread.

If lowest cost is your objective, you should take a look at the tb6560 chip. It cost less about $2, is readily available and is much simpler than what you have in mind. BUT, be sure to sequence the power supplies as specified by the datasheets, or the chip will self destruct.