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18 Installing and Configuring the HP E1459A
Front Panel Markers All "Data Available" and "Edge Detect" marker bits are physically available
via the HP E1459A front panel. These outputs are TTL/HC compatible and
may be used to trigger other system-wide events or to provide logging
information for statistical tracking or other performance analysis purposes.
Interrupt Driven or
Polled Mode
Operations
Interrupts may be programmatically disabled for both edge-detect and
data-capture events. All registers remain active and valid and may be
serviced on a polled mode basis.
Interrupt Parsing Since the command module interrupt handler must service multiple,
concurrently-occurring interrupts, (including those which may be sharing
the same IRQ line), some method is necessary to ensure that only a single
IRQ is posted by the HP E1459A during each service interval.
Individual interrupts must be serviced by a commander on a one-for-one
basis. The HP E1459A accomplishes this by inhibiting the generation of a
second IRQ each time an IRQ is posted. THE INHIBIT CONDITION IS
CLEARED BY THE REMOVAL AND REASSERTION OF EITHER
INTERRUPT ENABLE BIT, "DAV" OR "EDGE DETECT." (Refer to
Figure 1-2.)
For this one-for-one interrupt parsing, the HP E1459A REQUIRES that a
global interrupt enable, either DAV or Edge Detect, be disabled and
reasserted within the context of the interrupt service procedure. Normally,
you would simply shut off interrupts at the top of the service procedure, and
would then re-enable them before returning from service. This is the
suggested usage, although this specific sequence is not necessary for proper
HP E1459A hardware function.