I have never
looked, there is that second serial port at TTL levels (th
TXDB and RSDB piads on the serial daughterboard). Does anything ever come
out of there in normal operation?
Only this evening I realized, based on your remark on the extra serial
port, that channel A is used for both host (HX-20) and 2nd TF-20 and
Yes. THe pass-thorugh to the second HX20 does not go via the serial chip.
The serial lines to/from the HX20 (converted to TTL levels) are switched
between the serial chip in the TF20 and the buffers for the next-unit socket.
The inter-processor link in the HX20 itslef is somewhat similar. There's
a serial port o nthe main CPU that can be switched either to the slave
CPU or to the serial socket for the disk drive, etc.
channel B is not used. So connecting my TTL-to-USB to
the TXDB and RXDB
and boot the TF-20: alas no output or any reaction to Enter, Esc or Ctrl-C.
By now I know the boot ROM does initialize channel B, but does not write
to it. Apparantly TFDos doesn't either.
Pity :-(
I don't know if there's any Digital Research code in the TF20 OS, but it
wouldn't suprise me, BTW. It seems to be very similar to CP/M.
-tony