19200 baud on the Unix PC serial port

[Mark Dapoz]

In article <1865 at neoucom.UUCP> wtm at neoucom.UUCP (Bill Mayhew) writes:
>If you look in /usr/include/sys/termio.h, you'll see both EXTA and
>EXTB defined.  EXTB is not suppoted by the kernel, according to a
>comment in termio.h; if EXTB worked, it would be for 38400 bps.

No, termio.h says B38400 is not supported, not that EXTB isn't supported.  I've
looked at the schematics for both the serial port on the motherboard and for
the combo card and both of them have circuitry there to allow the uart to
accept an external clock signal.  The transmit clock is fed from pin 15 on the
DB25 and the receive clock is on pin 17.  I was thinking of trying to generate
a clock signal for 38.4K baud which I could feed into these pins, but then I
realized that I don't know what clock frequency I need since I don't know what
constant the kernel used in the 8530 baud rate generator when set to EXTB.
Has anyone ever used these external clock pins before?  Anyone know what time
constant is used for EXTB?
-- 
  Mark Dapoz  (mdapoz at hybrid.UUCP)  ...uunet!mnetor!hybrid!mdapoz

I remind you that humans are only a tiny minority in this galaxy.
	   -- Spock, "The Apple," stardate 3715.6.