Apple Lisa - Page 56

Confidential
INTn/
Lisa Hardware Reference Manual 7-Jul-81
INTn/ is the Interrupt output from the expansion
board to the 68000. When an expansion device
interrupts the system, INTn/ should be held low
until it is reset by the 68000.
IAKn/
When the 68000 recognizes the INTn signal, it
asserts the Interrupt Acknowledge signal.
IAKn/ is asserted when AS is asserted, so to
provide a 68000 interrupt vector, the vector
is applied to the bus and a DTACK/ signal is
generated. If an autovector cycle is desired,
the lAKn/ signal is routed to the VPA/ signal,
and the 68000 provides the interrupt vector,
depending on which slot the interrupt is provided
for. To insure that a Bus Error does not occur,
an I/O card should always provide an interrupt
vector, even if it doesn't think it asserted
the interrupt line. To keep spurious interrupts
from crashing the system, the interrupt handler
should test each in~errupt source on the I/O
card, and should return from the inter~lpt
if the card did not cause the interrupt.
SLn/, SHn/ The ~o select signals for each expansion slot
select contiguous 2048 word sections of memory.
SLn/ selects the low 2048, and SHn/ selects the
high 2048 words. The select lines are asserted
after the the addresses are valid, and remain
asserted until the data bus can be tri-stated
on a read cycle.
Power Supplies
The I/O cards are provided with four voltages
from the power supply: +12, +5, -5, and -12 volts.
Both Digital and Analog Grounds are brought to
the board. All three expansion I/O cards can
draw a
maximum of 75 ma from the -5 volt line,
and a maximum of 100 ma from the -12 volt line.
The cards can draw up to 10 watts from the other
lines.
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