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FUNCTIONAL DESCRIPTION
The PIC-8 Priority Interrupt-Programmable Clock board
provides the IMSAI 8080 Microcomputer System an eight
level Priority Interrupt capability and a software-
controlled interval clock.
The Priority Interrupt system utilizes the Intel 8214
Priority interrupt control unit and monitors the 8 Priority
Interrupt lines on the 8080 back plane.
capability to service either single or multiple interrupt
requests.
When enabled and receiving an interrupt request,
the Pic-8 determines if the request priority is higher
than the software-controlled current priority, and if
necessary issues a restart instruction that directs the
8080 system to one of eight priority controlled restart
locations.
For multiple interrupt requests, the 8214
determines the highest priority request, and processes it
normally.
It should be noted that the system does not store
inactive requests, and that a peripheral device must hold
an interrupt request until it is serviced by the
microprocessor.
The current priority status register may be software set to
any value desired to prevent low priority interrupts from
being generated until the priority status register is reset
to a lower value.
it is desired for all levels of interrupt to always occur.
The PIC-8 board also includes a clock circuit which provides
programmed control at intervals ranging from .1 millisecond
to 1 second.
The program can select from among 3 jumper
selected interval rates, or it can turn all three off.
3 rates are jumper-selectable to any of the following
values:
.1 ms, .2 ms, 1 ms, 2 ms, 10 ms, 20 ms, 100 ms,
200 ms, or 1000 ms.
OUTPUT port is connected to a transistor and jumper pads
for a special-purpose programmer-controlled output.
is provided on the circuit board for a small speaker or
other, user-supplied circuitry.
IC hole patterns with power and ground decoupling for special
purpose user circuits.
accept wire wrap sockets.
Power on the board is regulated by an integrated circuit
power regulator with current limiting protection.
ceramic bypass capacitors are supplied with the board.
board is G10-type double-sided laminate with plated throuqh
holes and contact fingers are gold-plated over nickel for
reliable contact and long life.
PIC-8
The status register may be set to 0 if
Additionally, one bit of the DATA
Also provided are 5 16-pin
These hole patterns are drilled to
£ u n c t i o n a i D e s c r i p t i o n
R e v i s i o n
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The PIC-8 has the
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