Specifications

56 Chapter 5 - Software Interface
Interrupt Mode
If Interrupt Mode is enabled either by jumpers or software setup, the controller
asserts the selected IRQ signal when data becomes available (as it clears the Not
Ready bit). It is not necessary for the host to poll the Not Ready bit in Interrupt
Mode. Upon interrupt, the host jumps to a corresponding interrupt service routine
(ISR) whose location is stored in its interrupt vector table. The ISR retrieves the
data from the controller and then returns to the interrupted process. A full
discussion on writing interrupt-driven code is language and operating system
dependent, and is beyond the scope of this manual. It is possible to setup the
controller through polling, then switch to interrupt-driven code to receive Touch
packets.
PC-Bus Interrupt Specifics
An IRQ signal can be used by only one device at a time in the PC architecture. It is
possible, however, for the E271-2201 PC-Bus controller to share an IRQ signal
with another device if the other device can release (tri-state) its interrupt line
drivers. Most serial and parallel controllers on the PC have this feature (see the
IBM Technical Reference Manuals).
To share an IRQ, the E271-2201 controller should be programmed to use the IRQ
only when the other device is tri stated. When the other device needs the IRQ, the
host must reprogram the E271-2201 to IRQ0 (Polled Mode). This way, only one
device is driving the interrupt line at a time.
The E271-2201 is shipped without an IRQ jumpered. For information on selecting
an interrupt, see Chapter 2. For the most flexibility, an interrupt-driven driver
should use the Parameter command (see page 95) to select an interrupt as the
driver is loaded.
Micro Channel Interrupt Specifics
Unlike the PC-Bus architecture, an IRQ signal can be shared by more than one
device in the Micro Channel architecture, although the rules for interrupt chaining
are not standardized under DOS. The E271-2202 Micro Channel controller is
capable of sharing an interrupt. (ELODEV does not support interrupt sharing
however).
The Not Ready bit, (bit 7 of the Base Port), can be used by an interrupt-driven
driver program to see if the E271-2202 generated the interrupt. Otherwise, the
driver can jump to the next interrupt service routine in the chain.
The E271-2202 controller is shipped without an IRQ selected. The IBM-supplied
Reference Disk will select a Base I/O Port and IRQ after examining the .ADF files