Using Interrupts; Configuring For Interrupts; Generating Interrupt Requests - HP E1399A User Manual

Using Interrupts

Configuring for
Interrupts
Generating
Interrupt Requests
44 Using the HP E1399A
The breadboard module can be configured to generate an interrupt to the
interrupt handler when service is required. (If you are not going to
implement the interrupt capability on your breadboard module, you must tie
the IRQ user access point to ground to prevent undesired interrupts.)
To configure the module to generate interrupts, you must first assign an
interrupt level to the module. Levels 1-7 are available, with level 7 being the
highest level. Connect a jumper in two places for the selected level, one for
the IRQ REQuest line and one for the IRQ ACKnowledge line. As shown in
Figure 2-12 (Chapter 2), jumpers have been installed to select interrupt level
1 (IRQ1*). Remember, both level selects must be the same.
To generate the interrupt request and accept the interrupt acknowledgment
from the interrupt handler, you must implement the following actions:
1. You must provide the interrupt request from your custom circuits by
setting the IRQ access point high (1) when the interrupt is to occur.
2. Monitor PIACK* after setting IRQ. After PIACK* goes low (true)
and before it goes high (false), release IRQ or another interrupt will
be generated.
3. If you do not implement the interrupter capability, leave the jumper
between IRQ and GND intact.
4. Your system controller and/or interrupt handler must react to the
signal timing in the Interface IC (U6) for the IRQ and DTACK state
machines as shown in Figure 3-5.
5. The circuitry provided implements a read operation for only the
lower 8 bits of status/ID during the interrupt acknowledge cycle,
using PIACK* to enable buffer U11. If you want to use the upper
8 bits also, you must provide an additional buffer to the internal data
bus that is enabled by PIACK* low (true) and DS1* low (true).
Chapter 3