Hardware manual

serial board it may not be able to use IRQs 8 and above.
Make sure you don't use IRQs 1, 6, 8, 13 or 14! These are used by your motherboard. You will make her very
unhappy by taking her IRQs. When you are done you might want to double-check /proc/interrupts
when programs that use interrupts are being run and make sure there are no conflicts.
8.9 Choosing Addresses --Video card conflict with ttyS3
Here's a problem with some old serial cards. The IO address of the IBM 8514 video board (and others like it)
is allegedly 0x?2e8 where ? is 2, 4, 8, or 9. This may conflict with the IO address of ttyS3 at 0x02e8. Your
may think that this shouldn't happen since the addresses are different in the high order digit (the leading 0 in
02e8). You're right, but a poorly designed serial port may ignore the high order digit and respond to any
address that ends in 2e8. That is bad news if you try to use ttyS3 (ISA bus) at this IO address.
For the ISA bus you should try to use the default addresses shown below. PCI cards use different addresses so
as not to conflict with ISA addresses. The addresses shown below represent the first address of an 8-byte
range. For example 3f8 is really the range 3f8-3ff. Each serial device (as well as other types of devices that
use IO addresses) needs its own unique address range. There should be no overlaps (conflicts). Here are the
default addresses for commonly used serial ports on the ISA bus:
ttyS0 address 0x3f8
ttyS1 address 0x2f8
ttyS2 address 0x3e8
ttyS3 address 0x2e8
Suppose there is an address conflict (as reported by setserial -g /dev/ttyS*) between a real serial
port and another port which does not physically exist (and shows UART: unknown). Such a conflict shouldn't
cause problems but it sometimes does in older kernels. To avoid this problem don't permit such address
conflicts or delete /dev/ttySx if it doesn't physically exist.
8.10 Set IO Address & IRQ in the hardware (mostly for PnP)
After it's set in the hardware don't forget to insure that it also gets set in the driver by using setserial. For
non-PnP serial ports they are either set in hardware by jumpers or by running a DOS program ("jumperless")
to set them (it may disable PnP). The rest of this subsection is only for PnP serial ports. Here's a list of the
possible methods of configuring PnP serial ports:
Using a PnP BIOS CMOS setup menu (usually only for external devices on ttyS0 (Com1) and ttyS1
(Com2))
•
Letting a PnP BIOS automatically configure a PnP serial port See Using a PnP BIOS to IO-IRQ
Configure
•
Doing nothing if the serial driver recognized your card OK•
Using isapnp for a PnP serial port (non-PCI)•
Using setpci (pciutils or pcitools) for the PCI bus•
The IO address and IRQ must be set (by PnP) in their registers each time the system is powered on since PnP
hardware doesn't remember how it was set when the power is shut off. A simple way to do this is to let a PnP
BIOS know that you don't have a PnP OS and the BIOS will automatically do this each time you start. This
might cause problems in Windows (which is a PnP OS) if you start Windows with the BIOS thinking that
Windows is not a PnP OS. See Plug-and-Play-HOWTO.
Serial HOWTO
What IRQs to choose? 35