[ICOM] CI-V bus collisions and the PW-1

[Dave AA6YQ]

Collisions can occur on the CI-V bus if two devices simultaneously transmit.
Since CI-V bus drivers are required to be "open collector", this isn't
doesn't pose an electrical problem, but it does result in corrupted
messages. In communication media where collisions can occur, the idea is
that

- a device that receives a corrupted message will ignore it

- a device that sends a message that was corrupted will either notice that
it was corrupted, or will notice the absence of a timely response and
re-transmit the message

If the corruption caused by a collision yields an invalid message, then this
message can be rejected. But if a collision transforms a "set your frequency
to 14,012.3" message into a "set your frequency to 37,426.8" message, the
device receiving this message will set its frequency to 37,426.8 instead of
14,012.3. If the application that sent the "set your frequency to 14,012.3"
message is monitoring the CI-V bus, then it can notice this corruption and
re-send the "set your frequency to 14,012.3" message, but in the mean time
the the device receiving the corrupted message has QSY'd to 37,426.8.

Back in 2006, I worked with Jamie W2QO to get his IC756Pro III and PW-1
working together with DXLab Commander, a transceiver control application. As
described on page 12 of the PW-1 manual, the transceiver's "CI-V transceive"
menu item is expected to be enabled, and the PW-1 must be programmed to
track the transceiver's frequency reports when its tuning dial is rotated
with "CI-V transceive" enabled. We discovered that if the PW-1 doesn't
receive a "frequency report" message at least once every 10 seconds, it
begins sending "report frequency" messages, which collide with messages
generated by the transceiver when its frequency dial is rotated, and with
messages generated by the transceiver control application. Messages
corrupted by these collisions cause the transceiver and PW-1 to jump around
in frequency as described above, even while transmitting.

Jamie solved this problem with a MicroHAM Band Decoder, which eliminated the
need to connect the PW-1 to the CI-V bus, and eliminated the need to enable
the transceiver's "CI-V transceive" menu item -- thereby eliminating all
sources of collisions.

It would be nice if Icom re-engineered the PW-1 to work correctly when the
connected transceiver is PC-controlled.

    73,

       Dave, AA6YQ