Specifications

E271-2201 PC-Bus Controller 19
Selecting the Interrupt (IRQ)
The E271-2201 may be operated in either Polled or Interrupt Mode. In Interrupt
Mode, the controller signals the host that data is available. In Polled Mode, the
host software must poll the controller for information.
To use Interrupt Mode, you may install jumpers at J2 and/or J3 to select the
Interrupt (IRQ). For Polled Mode, neither jumper should be installed.
Interrupt J2 J3
None (polled) none none (shipped setting)
IRQ5 installed none
IRQ3 none installed
IRQ2 installed installed
IRQ7 ----cross connected----
A software command may also be used to select a wider range of Interrupt values.
Any Interrupt from IRQ2 to IRQ7 can be used. The Interrupt can be saved in
NVRAM as a power-on default. See the Parameter command, page 95, for
details. If you are using Elo driver programs, jumper the controller for Polled
Mode as the IRQ is selected by software setup (unless E271-141 emulation mode
is selected with J10).
Choose the Interrupt carefully so it is not the same as another device.
The following table lists the devices assigned to each interrupt in a PC/XT and a
PC AT:
IRQ XT AT/386/486
2 IBM EGA, IBM network Mapped to IRQ9
3 COM2 COM2
4 COM1 COM1
5 Hard disk controller LPT2
6 Floppy disk controller Floppy disk controller
7 LPT1 LPT1
Elo's recommendations for choosing an interrupt, in order of preference, are listed
below. Compare these interrupts with the tables above, skipping the interrupt if a
conflict exists.
XT: 7,3,4,2,6,5 AT/386/486: 5,7,2,3,4,6
To avoid any chance of interrupt contention, you should design the driver software
to disable the interrupt line drivers of contending devices where possible, such as
serial and parallel controllers.