rtd DM5816, User Manual

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DM5816/DM6816 RTD Embedded Technologies, Inc.
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Chapter 7 – Interrupts
This chapter explains P14 jumper selectable interrupts and basic interrupt programming
techniques.
The DM5816 has one interrupt circuit which can generate interrupts on any IRQ channel 2
through 15, depending on the setting of the jumper on P4 or P16.
P14: Jumper Selectable Interrupts
The DM5816 circuitry has four jumper selectable interrupt sources which can be set by
installing a jumper across the desired pair of pins at P14.
To use these interrupts, an interrupt source must be jumpered on P14, an interrupt channel
must be jumpered on P4, and the IRQ enable must be set high (BA + 16, bit 0). BA + 16, bit 1
sets the polarity of the interrupt.
Selecting the Interrupt Channel
The IRQ channel is selected by installing a jumper on header connector P4 or P16 across the
desired pair of pins, as described in Chapter 1. A jumper is also installed across the G pins if
you are using the interrupt sharing feature.
Interrupt Sharing
This module is capable of sharing interrupts with multiple modules. This circuit is described in
chapter 1. If you are not planning on using shared interrupts or you are not sure that your CPU
can support shared interrupts, you should disable this sharing circuit by setting bit 2 at BA + 16
to a "1". By doing this the board works in normal interrupt mode and is compatible with all
CPUs.
Basic Programming for Interrupt Handling
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 very handy for dealing with asynchronous events (events that occur at less than
regular intervals). 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 for it to do nothing while waiting
for a keystroke to occur. Thus, the interrupt scheme is used and the processor proceeds with
other tasks. Then, when a keystroke does occur, the keyboard ‘interrupts’ the processor, and
the processor gets the keyboard data, places it in memory, and then returns to what it was
doing before it was interrupted. Other common devices that use interrupts are modems, disk
drives, and mice.