At 09:35 PM 4/21/2001 -0400, you wrote:
>>You do need 2 pwm outputs for each H bridge, both are not running at the
>>same time though :-)
>>>An '876 is definitely a better processor for this application.
>
>Or 1 PWM per h-bridge and a DIRection bit.  Feed the direction
>bit to an AND gate, as well as through an inverter to another AND.
>The second input to each AND is a PWM signal.  This prevents
>the program from turning both sides of the H-bridge on at the
>same time, and makes the 877's dual PWM output able to drive
>2 (bi-dir) H-bridges.

Not if you use the capture channels for measuring the servo pulses, you
can't have 2 captures and 2 PWM. That's why I did the PWM in software.
Although I've never had both directions turn on at once, if you design your
H-bridge correctly(it only takes 2 small transistors extra) you can prevent
shorts and get a braking channel for "free".

-Bob

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