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2.4.1 Interrupt Request (IRQ7–IRQ1)
Three input signals (IRQ7, IRQ4, IRQ1) notify the core processor of an interrupt request.
Four additional interrupt request lines (IRQ6, IRQ5, IRQ3, and IRQ2) are shared with
parallel port B pins and may be individually programmed as interrupts.
IACK7
IACK1
2.4.2 Interrupt Acknowledge (
–
)
Three output signals (IACK7, IACK4, IACK1 ) indicate an interrupt acknowledge cycle.
Four additional interrupt acknowledge lines (IACK6, IACK5, IACK3, and IACK2) are
shared with parallel port B pins and may be individually programmed as interrupt
acknowledges.
2.4.3 Port A Signals (PA7–PA0)
These eight pins serve as port A parallel input/output signals.
2.4.4 Port B (PB7–PB0)
These eight pins are shared with IRQ6, IRQ5, IRQ3, IRQ2 and IACK6, IACK5, IACK3,
IACK2, and can be individually programmed to serve as port B parallel input/output
signals.
2.5 CLOCK AND MODE CONTROL SIGNALS
These four pins are used to connect an external crystal to the on-chip oscillator and define
the four multifunction pins.
2.5.1 Crystal Oscillator (EXTAL, XTAL)
These two pins are the connections for an external crystal to the internal oscillator circuit.
If an external oscillator is used, it should be connected to EXTAL, with XTAL left open,
and must drive CMOS levels. A crystal or clock input must be supplied at all times.
2.5.2 Clock Out (CLKOUT)
This output signal is the system clock output and is used as the bus timing reference by
external devices.
2.5.3 Address Mode (AMODE)
This input signal provides mode control for the multi-function chip select pins. When set to
zero, A23–A20 is selected and when set to one, CS7–CS4 is selected. The mode
selection is static: AMODE is latched at the end of any system reset.
2.6 SERIAL MODULE SIGNALS
The following paragraphs describe the signals used by the serial module on the MC68306.
2-10
MC68306 USER'S MANUAL
MOTOROLA
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