From: John Kim (jokim_at_CHS.CUSD.CLAREMONT.EDU)
Date: Mon Jan 10 1994 - 03:35:38 EST
Since nobody else has mentioned, the MegaHertz V.32bis PCMCIA modem emulates
a 16450 UART, not a 16550AFN UART. A couple competitors have the 16550,
namely, IBM, AT&T, and Practical Peripherals. The built-in serial port on
the 750 only has a 16450 too, which I'm using with an external modem. It's
not fun, although I'm beginning to suspect the OS/2 comm drivers are partly
at fault (it works fine in some programs and at certain buad rates, but not
others).
What's a 16450/16550 UART? The UART is a buffer that holds data going to/
coming from your serial port. That way, the CPU doesn't get 14,400
interrupts each second if you're doing a 14.4kbps file transfer. The 16450
has an 8 bit buffer which was fine back in the 2400bps 80286 days, but tends
to suffer overruns (bad packets in a file transfer) at 9600+bps, especially
if you're multitasking. The 16550 has a 16-bit buffer that seems to work
fine with 14.4kbps modems while multitasking.
Megahertz says they're working on a model that emulates a 16550.
On the matter of the serial port on the 750, is anybody else using it with
an external 14.4kbps modem? I tend to lose characters when I use a 14.4kbps
connection, but 9600 bps works fine. Then I happened to connect at 9600 bps
while the processor speed was set to slow (18 MHz) and it still worked fine.
That makes me suspect 14.4 should work fine at 33 MHz, but it doesn't.
-- John H. Kim | "In fact, Chicago does support security. The sec- jokim_at_jarthur.cs.hmc.edu | urity APIs are there; they just don't do anything." This mail sent by NUPop | - Brad Silverber, VP Microsoft personal systems
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