schoff@BBN-UNIX@sri-unix.UUCP (08/31/83)
From: Martin Schoffstall <schoff@BBN-UNIX> I bought a Quadram board with 2 RS232 ports on it, why can't I use both ports? Even worse, I have two Quadram boards if I enable COM1 on one and COM2 on the other it doesn't seem to work on either? Any suggestions? schoff at bbnu
GILLMANN@USC-ISIB@sri-unix.UUCP (08/31/83)
From: Dick Gillmann <GILLMANN@USC-ISIB> The problem is that the two ports must be on different interrupt levels. When the PC was released there wasn't a definition of COM2: included. AST took the route of leaving jumpers that could put COM2: on any of several interrupt levels. Quadram (at least my (early) board) puts all serial ports on level 4, which is COM1:. The latest serial ports from IBM can be switched from COM1: to COM2: by flipping a little jumper plug. In COM2: mode they are on level 3 (level 5 is used by the XT's hard disc). So I suppose this is official: COM1: is on IRQ4 and COM2: is on IRQ3. If you have two ports on the same level, they fight, i.e. one tries to raise an interrupt while the other tries not to. This leads to some strange behavior. Generally you'll get one character through and then hang. This problem only happens with interrupt driven I/O on the serial ports. The BIOS, which does busy waits, is not affected. /Dick Gillmann -------
BILLW@SRI-KL@sri-unix.UUCP (08/31/83)
Some boards do not enable interupts for the second RS-232 port. I tried this out as I was developing a (commercial) communications package for the IBM PC, and found that the interrupt pin on the second 8250 on a (argh! can't remember the company name. It was a 256K memory + 2 serial port board) wasn't connected to ANYTHING! The reasoning behind this (I assume) is that if you have multiple chips generating a single interrupt, then you can't trivially figure out which port the interrupt was actually for. In particular, interrupt driven software that assumes only one active port is likely to break. Bill Westfield
sigurd@udel-relay@sri-unix.UUCP (08/31/83)
From: sigurd@udel-relay (ANDERSEN) You may be having some problem due to the fact that the Quadram II (the board with two RS-232 ports) does NOT work identically to the IBM asynch. boards. Someone here bought about 20 of the boards, only to find that they wouldn't work with one of their printers. Even with one serial port enabled and configured just like the IBM port had been, the system would hang when trying to print. Disab- ling both Quadram ports and using the IBM board would work OK. After much back and forth, Quadram admitted that the above is true. I haven't heard yet what, if anything, Quadram plans to do on this. - Sigurd Andersen (sigurd@udel-relay)