On Sat, 19 May 2018 11:31:11 +0000 (UTC), Martin Gregorie wrote:

>>> FWIW the target device is a Dittel KRT2 airband tranceiver.
>>
>> Have you checked that it setting the hardware handshake lines
>> correctly?
>
> There aren't any: the AXE027 USB-serial adapter uses a three wire
> connection terminated by a 3.5mm stereo jackplug.

This is probably very close to a saying involving Grandmas and eggs
but:

Is the KRT2 also a three wire device (Tx, Rx, Gnd)? Or does it expect
to  see any handshake lines? Though TBH I wouldn't expect it to work
in either direction if it expected hardware handshake.

As the AXE027 is designed for a PICAXE is it using TTL 0 - 5 V signal
levels or proper RS232 +/- 12 V? What does the KRT2 expect?

Can you monitor the Tx and Rx an lines and see if data is being sent
on either. A LED with series resistor from each line to Gnd will do.
Once you know that the hardware is playing you know for certain that
you have a software problem of some sort.

--
Cheers
Dave.

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