mc68hc05pl4b Freescale Semiconductor, Inc, mc68hc05pl4b Datasheet - Page 28

• Manufacturer Part Number: mc68hc05pl4b
• Description: Low-cost Single-chip Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

GENERAL RELEASE SPECIFICATION
4.3
4.4
4.4.1 LED/IRQ Pin
4-4
SOFTWARE INTERRUPT
The software interrupt (SWI) instruction causes a non-maskable interrupt.
EXTERNAL INTERRUPT
The LED/IRQ pin is the source that generates external interrupt. Setting the I bit in
the condition code register or clearing the IRQEN bit in the miscellaneous control/
status register disables this external interrupt.
This pin is an open drain pin and setting the IRQEN bit in Miscellaneous Control/
Status Register (MICSR) will set this pin for external interrupt input pin.
An interrupt signal on the LED/IRQ pin latches an external interrupt request. To
help clean up slow edges, the input from the LED/IRQ pin is processed by a
Schmitt trigger gate. When the CPU completes its current instruction, it tests the
IRQ latch. If the IRQ latch is set, the CPU then tests the I bit in the condition code
register and the IRQEN bit in the MICSR. If the I bit is clear and the IRQEN bit is
set, then the CPU begins the interrupt sequence. The CPU clears the IRQ latch
while it fetches the interrupt vector, so that another external interrupt request can
be latched during the interrupt service routine. As soon as the I bit is cleared dur-
ing the return from interrupt, the CPU can recognize the new interrupt request.
Figure 4-3 shows the logic for external interrupts.
The LED/IRQ pin can be negative edge-triggered only or negative edge- and low-
level-triggered. External interrupt sensitivity is programmed with the IRQS bit.
With the edge- and level-sensitive trigger option, a falling edge or a low level on
the LED/IRQ pin latches an external interrupt request. The edge- and level-sensi-
tive trigger option allows connection to the LED/IRQ pin of multiple wired-OR
interrupt sources. As long as any source is holding the LED/IRQ low, an external
interrupt request is present, and the CPU continues to execute the interrupt ser-
vice routine.
With the edge-sensitive-only trigger option, a falling edge on the LED/IRQ pin
latches an external interrupt request. A subsequent interrupt request can be
latched only after the voltage level on the LED/IRQ pin returns to a logic one and
then falls again to logic zero.
To use the external interrupt function to exit from WAIT or STOP, it must be
enabled prior entering either of the power saving modes.
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
April 30, 1998
INTERRUPTS
NOTE
MC68HC05PL4
REV 2.0