At 06:01 PM 1/20/97 +0200, you wrote:


>On my PC I have 4 COM ports, and I can set the IO card to what I want, but
>95 insist that COM3 stay on IRQ4, and COM4 on IRQ5. (Useless info : When I
>stick a modem on COM4 it talks to it, but the modem response isn't seen.) If
>however, I stick it on COM3, the same IRQ as COM1, my mouse, using the modem
>makes the mouse hang up. If I stick PIC comms there, the mouse hangs up, but
>the PIC talk isn't received unless you move the mouse !


I bought a serail add in card (ISA) with two serial ports on it.  I set the card
to use COM3 and COM4 for the I/O addresses and IRQ 11 and IRQ 12 for the
interrupts.  Stuffed the board in, and let windows 95 find the new hard
ware.  It got both the I/O and IRQ settings correct, even though it was not
a plug
and play card.  Port's are up and running.  Do no try to set two UARTS on
the same IRQ, because the 8259 in the PC is set for edge detection, you're sure
to drop one and hang the system.


If you know what you're doing, you can modify the UART board IRQ lines for wired
OR operation, but I suspect this still requires special code in the driver.

Another thing to watch out for is providing stack space for the interrupt
handler.  DOS and the BIOS code don't always have a lot of stack space
availible, so it's best to install a small stack for each UART.  Set aside
the space in the code segment, and you'll have it availible as soon as the
interrupt handler starts running.

I've got a lot of serial code written in C for handling a single serial
port.  After looking at the problems I've started working on a package to
support 4 serial ports written in Turbo Assembler.  Everybody should have
some Serial code in their back pocket to carry around, it's very useful stuff.

WB4ZUY@amsat.org