Motorola M68EM05P18, User Manual

Page: 28 / 56

MMDS/MMEVS Configuration and Operation
MC68HC(8)05P18 Emulation
M68EM05P18UM/D
28 MMDS/MMEVS Configuration and Operation MOTOROLA
Port A Pullups/
Interrupts In single-chip mode operation:
The simple port A input/output (I/O) feature and the associated
interrupt/pullup options are implemented through the port A pins of
the MC68HC(8)05P18 MCU. With this implementation, an interrupt
service routine could poll the external IRQ pin using BIL and BIH
statements and determine if the source of an interrupt was the
external IRQ pin or one of the enabled port A interrupts.
In emulation:
The port A I/O function is rebuilt off-chip and the enabled
interrupt/pullup options will generate interrupts through the external
IRQ pin. An interrupt service routine using BIL and BIH instructions
could not determine if an interrupt was generated via an external IRQ
pin or one of the enabled port A interrupts. The proper way to
differentiate between a port interrupt and external interrupt is to have
the interrupt service routine poll possible port A interrupts and, if none
are low, then the interrupt was driven by an external IRQ.