STC12C5Axx
Technical Summary
67
POWER-DOWN Mode
An instruction setting
PCON
.1 causes the device go into the
POWER-DOWN
mode. In the
POWER-DOWN
mode, the on-chip oscillator is stopped. The contents of on-chip RAM and
SFRs are maintained.
The power-down mode can be woken-up by either pin RST event or interrupt from INT0 or
INT1. When it is woken-up by RST, the program will execute from the address 0x0000. Be
carefully to keep RST pin active for at least 10ms in order for a stable clock. If it is woken-up
from pin INT0 or INT1, the CPU will rework through jumping to related interrupt service routine.
Before the CPU rework, the clock is blocked and counted until 32768 in order for de-bouncing
the unstable clock. To use INT0/INT1 wake-up, interrupt-related registers have to be enabled
and programmed accurately before entering power-down.
Pay attention to add at least one
“NOP” instruction subsequent to the power-down instruction if I/O wake-up is used.
SFR:
PCON
(Power Control)
Read/Write
Address:
0X897H
Default: XXXX-X000
Bit
7
6
5
4
3
2
1
0
Name SMOD SMOD0
LVDF POF
GF1 GF0 PD IDL
SMOD: =
Double baud rate of UART interface
0
: =
Keep normal baud rate when the UART is used in mode 1,2 or 3.
1
: =
Double baud rate when the UART is used in mode 1,2 or 3.
SMOD0:=
SM0
/
FE
bit select for SFR
SCON
.
7
; Setting this bit will set SFR
SCON
.
7
as Frame Error function.
Clearing it to set SCON.7 as one bit of UART mode selection bits.
(This bit is serial port related, see the further description about the serial port)
LVDF: =
Low-Voltage Flag
After power-up, this bit will be initially set. The user should clear it by his program.
Continuously on operating, it will be set if the power supply drops under 3.7V/2.3V
(Operate in the 5V/3V).
POF: =
Power-On flag
This bit will be set after the device was powered on.
It must be cleared by the user’s software.
PD: =
Power-Down switch
Set this bit to drive the device enter
POWER-DOWN
mode.
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