34 Manual Document# 3PXCC4A3001
B&B Electronics Mfg Co – 707 Dayton Rd - PO Box 1040 - Ottawa IL 61350 - Ph 815-433-5100 - Fax 815-433-5104
B&B Electronics Ltd – Westlink Comm. Pk – Oranmore, Galway, Ireland – Ph +353 91-792444 – Fax +353 91-792445
Table 3. Frequently Unused Port Addresses
The IRQ is a hardware Interrupt Request line in an ISA bus
expansion slot on a PC or AT compatible computer. The 8 bit PC
ISA slot has 8 interrupts, the 16 bit slot has another 7 since one of
the first 8 is used to link in the remaining 8. The IRQ is used by
devices to request immediate service by the main microprocessor.
When the IRQ line is set, the microprocessor stops whatever it’s
doing, saves status, checks which line was set, then jumps to code
to handle the interrupt. The processor then clears the interrupt and
returns to what it was doing before. IRQ lines are set by the internal
timer, keyboard, hard drive controller, PCI, USB controller, sound
card, serial ports, printer and more.
The 3PXCC4A cards allow the use of interrupts (IRQ) 2, 3, 4, 5,
6, 7, 10, 11, 12, 14, and 15. Table 4 shows the standard serial port
IRQ settings. Note: If two ports use the same IRQ setting, both ports
cannot use the serial port at once. Only one port at a time may
communicate.
Table 4. Standard IRQ Settings
Base
Hex
Address
Binary
Equivalent Switch
Settings
MSB LSB
7654321
I/O Space
Description
200 1000000000 1000000 game port
208 1000001000 1000001 game port
300 1100000000 1100000 prototype
308 1100001000 1100001 prototype
310 1100010000 1100010 prototype
318 1100011000 1100011 prototype
380 1110000000 1110000 SDLC
388 1110001000 1110001 SDLC
3A0 1110100000 1110100 bisync com
3A8 1110101000 1110101 bisync com
COM1 IRQ4
COM2 IRQ3
COM3 IRQ4
COM4 IRQ3