My trusty kit built SPROG, which I have been using for a few years now, has
suddenly developed a strange fault.

The initial symptom is that when querying the firmware version, Decoder Pro
reports that it is not connected to a Sprog, then returns the firmware version
correctly. It repeats this twice.

Then it cannot query any decoder (although the motor pulses as normal), and
trying to read back CVs returns 255 for all.

At first I suspected the ACK sense circuit for the latter problem, but then I
tried talking directly to Sprog with Hyperterminal.

What I discovered was that everything seems to be working normally except that
the returned prompt has become:

P> PP>

I'm sure this is not how it normally is - am I correct?

Presumably the extra P's are confusing Decoder Pro.

If I press the Sprog reset button, the normal startup sequence is shown but with
the extra P's as follows:

SPROG Ver 3.9
P> PP>

I have mode set to 0800 and can get confirmation of this with the M command.

If I turn on track power with a + command, the prompt becomes just:

P>

As soon as I turn it off again with a - command, it reverts again to:

P> PP>

Apart from the strange prompts, all the commands for writing and reading CVs etc
seem to work fine, but of course Decoder Pro cannot communicate with the extra
prompt chars messing it up.

Any help appreciated!

Thanks,

Pete