Dealing with Limited IRQs
A fully equipped contest station uses serial ports for more functions than your PC has
IRQs to handle. Between rig control, sending CW, packet and RTTY interfaces you might need
4 or 5 serial ports. Plus you're also going to need IRQs for your CDROM, at least
one for a sound board and one for a mouse along with the usual IRQ requirements for a
floppy drive and hard disk.
On the single PC system at W5XD, all of the following can be operated simultaneously
(and in fact are in simultaneous operation as I type this): full rig control on two rigs
simultaneously, packet connection to the local DX cluster, RTTY on both rigs
simultaneously, connection to the internet, and fully networked logging onto a Ethernet
connected-laptop PC. You can configure your PC to do this, too.
The WriteLog contest logging system has a solution to this problem based on the
software and hardware conventions that have evolved for Windows products. DOS products,
however, don't benefit from these advancements.
Start with using an Ethernet card for networked mult-transmitter connections, and run
WriteLog on each PC with copies of the log repeated via the Ethernet. There are many cards
available and any that has an appropriate Windows driver will do the job for WriteLog.
"Appropriate" means a Windows for Workgroups 3.11 driver or Windows 95 driver.
These cards use at most one IRQ, and PCI versions, while more expensive, are available
that need no dedicated IRQ. The cheapest of the ISA network cards are available for $20.00
or so.
For serial port support, the first thing to understand is that there exist very
inexpensive 8-bit COM port cards that will add COM3 and COM4 to an existing PC already
populated with the standard COM1 and COM2 but that share IRQ 3 and IRQ 4 with the existing
ports. As a rule, these cards will not work with Windows 3.1 or Windows 95 software or
even with some DOS software, because these operating systems (along with many DOS
programs, e.g. CT) require a separate IRQ for each COM port.
There also exist 16 bit cards that provide additional COM ports, This is a solution to
the shared IRQ problem for COM ports, but my machine has no where near enough IRQs to run
six COM ports simultaneously this way. I suspect not many do.
Here's the layout at W5XD:
COM ports:
The COM port solution is to use a smart multi-port card for your COM ports. I use a RocketPort Quad/DB9 ISA adapter. In my Windows 95
system, this adapter provides 4 COM ports and uses no dedicated IRQ. (Take a look at the
DB-25 version as an equal-cost alternative. It has 25 pin connectors instead of 9 pin.) An
additional bonus is that the card is extremely high performance: it can handle 4
simultaneous 115K bps connections! It comes with an appropriate driver for Windows 95 and
one for Windows 3.11 as well, although I have made no attempt to test that configuration.
A similar board is available for PCI bus, but it costs much more and I haven't tested it
either.
The bad news is that the board is rather expensive, but don't pay full retail. I got
mine from Essential Data. They'll take your
credit card over the 'net and get the board to you overnight.
Limitations:
When running WriteLog with the RocketPort adapter, you cannot run RTTY using Baudot
modes on a dumb TU because the board does not support 5 bit codes. Note that PK-232
support is not affected, and operation on the usual COM1/COM2 built-in ports is not
affected.
