On Thu, Aug 01, 2002 at 03:55:07PM +0100, Trevor Page wrote:
> Hi list.
>
> I have an application where I need to generate a relatively large number of
> (slow) PWM signals. I'm not sure how many at the moment, but we could assume
> this number would far exceed the number of available IO on a PIC. Actually,
> the fact that it is PWM is probably not relevant. Let's just say that I need
> to expand the IO of my PIC. I don't need bi-directional IO. All I want to do
> is generate a large number of PWM signals, which will be low-pass filtered
> to get some crude analogue control voltages.
>
> The most obvious solution to me at the moment is through the use of a number
> of octal / hex latch ICs, such as the 40174. On the other end of the scale,
> I could use a Xilinx CPLD if I wanted to go mad (and needed the speed, which
> I don't).
>
> Can anyone suggest their own favourite solution for expanding IO on a PIC,
> to get a large number of digital outputs? Any particular device I should
> consider looking at?

The 74HC595 is a popular choice. 8 latchable, tristatable outputs that are
serially loaded. Can be laid end to end to create a large number of outputs.
Any number of outputs can be controlled by 3 PIC pins (data,clk,latch).

BAJ

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