Z87C33 Datasheet, PDF (25/72 Pages) Zilog, Inc. – CMOS Z8® MCU Consumer Controller Processor

Z87C33
CMOS Z8“ MCU Consumer Controller Processor
19
When more than one interrupt is pending, priorities are resolved by a programma-
ble priority encoder that is controlled by the Interrupt Priority register. An interrupt
machine cycle activates when an interrupt request is granted. This action disables
all subsequent interrupts, saves the Program Counter and Status Flags, and then
branches to the program memory vector location reserved for that interrupt.
All Z8 interrupts are vectored through locations in the program memory. This
memory location and the next byte contain the 16-bit address of the interrupt ser-
vice routine for that particular interrupt request. To accommodate polled interrupt
systems, interrupt inputs are masked and the Interrupt Request register is polled
to determine which of the interrupt requests require service.
When in ANALOG mode, an interrupt resulting from AN1 maps to IRQ2, and an
interrupt from AN2 maps to IRQ0. Interrupts IRQ2 and IRQ0 may be rising, falling,
or both edge-triggered, and are programmed in the IRQ register. The software
polls to identify the state of the pin. When in ANALOG mode, IRQ1 is generated
by the Stop-Mode Recovery source selected by SMR Register bits D4, D3, D2, or
SMR2 D1 or D0.
Programming bits for the Interrupt Edge Select are located in the IRQ register, bits
D7 and D6. The configuration is indicated in Table 7.
Table 6. IRQ Register*
IRQ
D7
D6
0
0
1
1
0
1
1
Notes:
F = Falling Edge
R = Rising Edge
Interrupt Edge
P31
P32
F
F
F
R
R
F
R/F
R/F
Clock. The Z8 on-chip oscillator features a high-gain, parallel-resonant amplifier
for connection to a crystal, LC, RC, ceramic resonator, or any suitable external
clock source (X_IN = INPUT, X_OUT = OUTPUT). The crystal should be AT-cut, 4
MHz maximum, with a series resistance (RS) of less than or equal to 100Ω when
oscillating from 1MHz to 4MHz.
The crystal should be connected across XTAL1 and XTAL2 using the vendor’s
recommended capacitor values from each pin directly to the device Ground pin to
reduce ground-noise injection into the oscillator. The RC oscillator option is mask-
PS015601-1003