
24
Using the Breadboard
Using the Interrupt
The Breadboard has a read only Interrupt Register located at address 04
h
in
A24 Memory. The contents of this register is used as an interrupt vector to
determine which interrupt source caused the interrupt.
If IACK* (Type C interrupt) is present, the content of the Interrupt Register
will be sent to the data bus and the IRQ* line will be released. Reading the
Interrupt Register will clear the interrupt request signal IRQ* to support
Type A interrupt.
Bits 2 through bit 15 of this register are not used. Bit 1 indicates an external
interrupt existing if the content of bit 1 is “1”. See Chapter 3, Register
Description for more information of this Interrupt Register.
IRQ* will be valid whenever the external interrupt occurs.
Figure 2-4 shows the timing for an interrupt acknowledge cycle.
Figure 2-4. Timing for Interrupt Acknowledge Cycle
SYSCLK
DS0*
DS1*
IACK*
DBEN*
DTACK*
MA(7:0)
MD(15:0)
IRQ*
(16MHz)
62.5 ns
62.5 ns
62.5 ns
190 ns
< 40 ns
62.5 ns
BUSY*
>0
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