GPS140 Datasheet, PDF (27/38 Pages) List of Unclassifed Manufacturers – GPS Positioning Module

INTERRUPTS
What is an interrupt?
An interrupt is an event that causes the processor in your computer to temporarily halt
its current process and execute another routine. Upon completion of the new routine,
control is returned to the original routine at the point where its execution was
interrupted.
Interrupts are a very flexible way of dealing with asynchronous events. Keyboard
activity is a good example; your computer cannot predict when you might press a key
and it would be a waste of processor time to do nothing whilst waiting for a keystroke
to occur. Thus the interrupt scheme is used and the processor proceeds with other
tasks. When a keystroke finally occurs, the keyboard then 'interrupts' the processor so
that it can get the keyboard data .It then places it into the memory, and then returns to
what it was doing before the interrupt occurred. Other common devices that use
interrupts are A/D boards, network boards, other used serial ports etc.
Your GPS140HR can interrupt the main processor when a satellite navigation data
message is received. You can write powerful code to interface to your GPS140HR
when you use interrupts.
Interrupt request lines
To allow different peripheral devices to generate interrupts on the same computer, the
PC AT bus has interrupt request channels (IRQ's). A rising edge transition on one of
these lines will be latched into the interrupt controller. The interrupt controller checks to
see if the interrupts are to be acknowledged from that IRQ and, if another interrupt is
being processed, it decides if the new request should supercede the one in progress
or if it has to wait until the one in progress has been completed. The priority level of the
interrupt is determined by the number of the IRQ as follows; IRQ0 has the highest
priority whilst IRQ15 has the lowest. Many of the IRQ's are already used by the
standard system resources, IRQ0 is dedicated to the internal timer, IRQ1 is dedicated
to the keyboard input, IRQ3 for the serial port COM2, and IRQ4 for the serial port
COM1. Often interrupts 2,5,7,10,11 and 15 are free for the user.
8259 Programmable Interrupt Controller
The chip responsible for handling interrupt requests in a PC is the 8259 Interrupt
Controller. To use interrupts you will need to know how to read and set the 8259's
internal interrupt mask register (IMR) and how to send the end-of-interrupt (EOI)
command to acknowledge the 8259 interrupt controller.
GPS140HR
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RTD Embedded Technologies, Inc.