On Thu, 29 Jan 1998 14:30:52 +0100, you wrote:

>Have anyone designed a one pin interface?
>
>It would be nice to have a simple monitor suopport program in every PIC, so
>if we want to check inside it when it is working (or working wrong) we can
>attach a specialised unit with a display and keyboard to it. We must use
>minimum number of pins for it (one), and it should be possible to implement
>"everywhere".
>
>The monitor unit I believe can be built using a F84, LCD and a few keys to
>select adress and view and change registers, force gotos or calls to
>stop,test,run routines etc in the target system.
>
>The target system«s routine shoud of course be as possible as possible, and
>perform som kind of erroer check so it don«t treat noise as instructions.
>
>The monitor scans the keys, decode it to simple instructions and send them
>to the target. The target sends back register contents binary, which the
>monitor decodes and displays.
I'd use half-duplex async, either using pin tri-stating or pseudo-open
drain. If the data is only sent 'on request' there's no uncertainty of
which direction you need at any given time.
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