mc68hc68t1 Freescale Semiconductor, Inc, mc68hc68t1 Datasheet - Page 20

• Manufacturer Part Number: mc68hc68t1
• Description: Mc68hc68t1 Real-time Clock Plus Ram With Serial Interface
• Manufacturer: Freescale Semiconductor, Inc

lowing:
MC68HC68T1
20
POWER–SENSING POWER–DOWN PROCEDURE
A procedure for power–down operation consists of the fol-
1. Set power sense operation by writing bit 5 high in the
2. When an interrupt occurs, the CPU reads the status
3. Sensing a power failure, the CPU does the necessary
interrupt control register.
register to determine the interrupt source.
housekeeping to prepare for shutdown.
NOTES:
AC LINE
1. The LINE input pin can sense when the switch opens by use of the power sense interrupt. The MC68HC68T1 crystal
2. For 32.768 kHz oscillator, see Figure 12. This configuration, when the MC68HC68T1 supplies the MCU clock, usually
3. If an MC68HC11 MCU is used, delete the capacitor at the RESET pin.
drives the clock input to the CPU using the CLKOUT pin. On power–down when V SYS < V BATT + 0.7 V, V BATT
powers the clock. A threshold detect activates an on–chip P channel switch, connecting V BATT to V DD . V BATT
always supplies power to the oscillator, keeping voltage frequency variation to a minimum.
requires a 1 to 4 MHz clock.
NOTE 1
REGULATOR
NOTE 2
BRIDGE/
Figure 19. Externally–Controlled Power System
11
14
15
13
LINE
V BATT
R CHARGE
MC68HC68T1
V DD POR
16
CLKOUT
4. The CPU reads the status register again after several
5. The CPU sets power–down (bit 6) and disables all
6. When power returns and V SYS rises above V BATT +
CPUR
V SYS
MISO
MOSI
milliseconds to determine validity of power failure.
interrupts in the interrupt control register when
power–down is verified. This causes the CPU reset and
Clock Out pins to be held low and disconnects the serial
interface.
0.7 V, power–up is initiated. The CPU reset is released
and serial communication is established.
SCK
10
INT
100 kΩ
SS
3
2
12
1
7
6
5
4
0.1
V DD
m
F
NOTE 3
39
28
31
32
33
2
1
IRQ
RESET
OSC 1
PORT (e.g., PC0)
MISO
MOSI
SCK
MC68HC05C4
40
V DD
MOTOROLA