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A specialized interface circuit enables the interconnection of a programmmable interrupt controller (for example, the Intel 8259) and a microprocessor (for example, the Zilog 2-80).
English (United States)
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Interfacing A Programmable Interrupt Controller Module To A
A specialized interface circuit enables the interconnection of a
programmmable interrupt controller (for example, the Intel 8259) and a
microprocessor (for example, the Zilog 2-80).
When the correctly initialized programmable interrupt controller receives an
interrupt command, it issues an interrupt (INT) signal to the microprocessor. The
interrupt controller expects to receive in response three interrupt acknowledge
(INTA) pulses from the microprocessor which it uses to strobe a 3-byte CALL
instruction onto the data bus for the microprocessor to execute.
The problem is that the microprocessor puts out only one interrupt
acknowledge pulse in response to the interrupt signal. The microprocessor
reads the first byte put on the bus by the interrupt controller, which is the CALL
operation code, and thereupon generates two read (RD) pulses to read the
remainder of the CALL instruction.
The interface circuit determines when an interrupt-acknowledge sequence
occurs and then transforms the two read pulses received from the
microprocessor into two additional interrupt acknowledge pulses going to the
interrupt controller. The interface also degates the two read pulses and prevents
transmission thereof to the interrupt controller. Concurrently with the two read
pulses the microprocessor transmits an address. All peripheral enables are
degated during an interrupt cycle to prevent any other device from...