Will tieing IN11 And IN21 to earth And IN12 and IN22 to Vcc drive the Stepper Motor or am I missing something.

BA6845FS Datasheet pdf - Magnetic Disk LSIs > FDD stepping motor driver - ROHM

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I don't see an internal oscillator, or other pulsing function on the IC, nor a spec on the rotation rate. It looks to me that you will have to supply the pulses to the inputs that stepper motors inherently require.

 

Pulses only to IN12 & IN22?

 

Pulses need to be applied to all four inputs. I think the pattern should be as follows:


22 21 12 11
1 H L H L
2 H L L H
3 L H L H
4 L H H L
5 H L H L

To reverse the direction of the motor, the pattern goes from steps 5 to 1, instead of steps 1 to 5.

 

IN11 And 21 are tied together on original PCB.

I thought the IC provided the pulses

IN11 12 21 22 are direction control only but pulling high and low the motor only gives a slight jog and manually pulsing +5v provides nothing more

 

Are you sure it is IN11 and IN21 that are tied together and not IN22 and IN12? If you look at the data sheet, IN22 and IN12 are always the same, while the other pair changes state.

I'm almost certain the IC does not provide the pulses. That is up to the user. It looks like the job of providing the input pulses is made somewhat easier by the control logic in the IC, though. I think two of the inputs can be held at a logic high (IN22 and IN12) while only the other two inputs need to be pulsed in the proper sequence.

The stepping sequence I gave in my post above is for the motor outputs. The trick is to find out what input (INxx)sequence gives that motor output sequence. You can do that by measuring the output state and writing down the input state for that output state. Direction is determined by the relative polarities of the outputs to the motor coils, and thus by the sequence of the input states. The direction column in the truth table in the data sheet is not the motor direction, but the direction of the current flow in the motor coils.

In any case I think you would do well to read up on how bipolar stepper motors work. Such as Jones on Stepping Motor Types

Just as an experiment tie IN12 and IN22 to logic 1. Then pulse inputs IN21 and IN11 in the following sequence:

IN21 IN11

0 0
0 1
1 1
1 0
0 0

If that does not work the first time, swap the wires on one of the motor coils and try it again.

 

I found this URL where a project is described using the same IC and an AVR. The same two input pins you saw tied together are also tied together in the project. This is due to the type of stepper motor, and the need to half-step it. It describes how the motor is stepped.


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fantastic
Really appreciate your help
Thanks