cdp68hc68t1 Intersil Corporation, cdp68hc68t1 Datasheet - Page 18

• Manufacturer Part Number: cdp68hc68t1
• Description: Cmos Serial Real-time Clock With Ram And Power Sense/control
• Manufacturer: Intersil Corporation

System Diagrams
NOTE: Example of a system in which the power is controlled by an external source. The LINE input pin can sense when the switch opens by use
of the POWER-SENSE INTERRUPT. The CDP68HC68T1 crystal drives the clock input to the CPU using the CLK OUT pin. On power down when
V
always supplies power to the oscillator, keeping voltage frequency variation to a minimum.
A Procedure for Power-Down Operation might consist of the following:
1. Set power sense operation by writing Bit 5 high in the Interrupt Control Register.
2. When an interrupt occurs, the CPU reads the Status Register to determine the interrupt source.
3. Sensing a power failure, the CPU does the necessary housekeeping to prepare for shutdown.
4. The CPU reads the Status Register again after several milliseconds to determine validity of power failure.
5. The CPU sets power-down Bit 6 and disables all interrupts in the Interrupt Control Register when power down is verified.
6. When power returns and V
SYS
This causes the CPU reset and clock out to be held low and disconnects the serial interface.
communication is established.
< V
BATT
+ 1.0V. V
LINE
BATT
AC
18
will power the CDP68HC68T1. A threshold detect activates a P-Channel switch, connecting V
(Continued)
FIGURE 17. EXTERNALLY CONTROLLED POWER SYSTEM DIAGRAM
SYS
rises above V
GENERATOR
BRIDGE
V
BATT
DD
CDP68HC68T1
, power-down is terminated. The CPU reset is released and serial
V
CDP68HC68T1
LINE
BATT
CLK OUT
CPUR
MISO
MOSI
V
POR
SCK
V
SYS
INT
CE
DD
V
DD
IRQ
RESET
OSC 1
PORT (e.g., PCO)
MISO
MOSI
SCK
CDP68HC05C8B
V
DD
BATT
to V
DD
October 29, 2007
. V
BATT
FN1547.8