MC68HC908QT4CPE Datasheet, PDF (50/192 Pages) Motorola, Inc – M68HC08 Microcontrollers

Auto Wakeup Module (AWU)
4.3 Functional Description
The function of the auto wakeup logic is to generate periodic wakeup requests to
bring the microcontroller unit (MCU) out of stop mode. The wakeup requests are
treated as regular keyboard interrupt requests, with the difference that instead of a
pin, the interrupt signal is generated by an internal logic.
Writing the AWUIE bit in the keyboard interrupt enable register enables or disables
the auto wakeup interrupt input (see Figure 4-2). A logic 1 applied to the
AWUIREQ input with auto wakeup interrupt request enabled, latches an auto
wakeup interrupt request.
Auto wakeup latch, AWUL, can be read directly from the bit 6 position of port A data
register (PTA). This is a read-only bit which is occupying an empty bit position on
PTA. No PTA associated registers, such as PTA6 data direction or PTA6 pullup
exist for this bit.
Entering stop mode will enable the auto wakeup generation logic. An internal RC
oscillator (exclusive for the auto wakeup feature) drives the wakeup request
generator. Once the overflow count is reached in the generator counter, a wakeup
request, AWUIREQ, is latched and sent to the KBI logic. See Figure 4-1.
Wakeup interrupt requests will only be serviced if the associated interrupt enable
bit, AWUIE, in KBIER is set. The AWU shares the keyboard interrupt vector.
COPRS (FROM CONFIG1)
AUTOWUGEN
SHORT
1 = DIV 2⁹
0 = DIV 2¹⁴
INT RC OSC
OVERFLOW
EN 32 kHz
CLK
RST
V_DD
D
Q
E
R
TO PTA READ, BIT 6
AWUL
AWUIREQ
TO KBI INTERRUPT LOGIC (SEE
Figure 9-3. Keyboard Interrupt
Block Diagram)
(CGMXCLK)
BUSCLKX4
RESET
CLRLOGIC
CLEAR
CLK
RST
RESET _ISTOP
RESET
ACKK
AWUIE
Figure 4-2. Auto Wakeup Interrupt Request Generation Logic
Data Sheet
50
Auto Wakeup Module (AWU)
MC68HC908QY/QT Family — Rev. 3
MOTOROLA