On its CAT/AUX connector an ACOM is the MASTER: it polls a transceiver and
changes band from the reply, so nothing can be pushed to it. internal/catemu
answers those polls on a second serial port, in ACOM command set 5 (Kenwood /
Elecraft): FA;, FB;, IF; and ID;, and nothing else — a wrong-length reply is
worse than none, it desynchronises the amp's parser for the following poll.
Also offered for SPE. Some amps do not poll at all but read the radio↔PC CAT
line in parallel; those never hear a responder, so an optional unprompted send
(500/1000 ms) covers them.
The TX frequency is what is sent: in split the amp must be tuned where we
transmit. Frame lengths are pinned by tests — the failure they guard against is
silent and only shows up as an amp that mistunes.
Untested on hardware.