at89c51rc-33pc ATMEL Corporation, at89c51rc-33pc Datasheet - Page 20

• Manufacturer Part Number: at89c51rc-33pc
• Description: 8-bit Microcontroller With 32k Bytes Flash
• Manufacturer: ATMEL Corporation

19. Power-down Mode
20
AT89C51RC
In the Power-down mode, the oscillator is stopped, and the instruction that invokes Power-down
is the last instruction executed. The on-chip RAM and Special Function Registers retain their
values until the Power-down mode is terminated. Exit from Power-down can be initiated either
by a hardware reset or by an enabled external interrupt. Reset redefines the SFRs but does not
change the on-chip RAM. The reset should not be activated before V
operating level and must be held active long enough to allow the oscillator to restart and
stabilize.
Figure 19-1. Oscillator Connections
Note:
Figure 19-2. External Clock Drive Configuration
Table 19-1.
Mode
Idle
Idle
Power-down
Power-down
C1, C2 = 30 pF ± 10 pF for Crystals
Status of External Pins During Idle and Power-down Modes
Program
Memory
Internal
External
Internal
External
= 40 pF ± 10 pF for Ceramic Resonators
ALE
1
1
0
0
OSCILLATOR
EXTERNAL
SIGNAL
NC
PSEN
C2
C1
1
1
0
0
PORT0
Data
Float
Data
Float
XTAL2
XTAL1
GND
XTAL2
XTAL1
GND
PORT1
Data
Data
Data
Data
Address
PORT2
CC
Data
Data
Data
is restored to its normal
PORT3
1920C–MICRO–03/05
Data
Data
Data
Data