AT89C51RB2/RC2
be the one following the instruction that puts the AT89C51RB2/RC2 into Power-down
mode.
Figure 34. Power-down Exit Waveform
INT0
INT1
XTALA
or
XTALB
Active Phase
Power-down Phase
Oscillator Restart Phase
Active Phase
Exit from Power-down by reset redefines all the SFRs, exit from Power-down by exter-
nal interrupt does no affect the SFRs.
Exit from Power-down by either reset or external interrupt or keyboard interrupt does not
affect the internal RAM content.
Note:
If idle mode is activated with Power-down mode (IDL and PD bits set), the exit sequence
is unchanged, when execution is vectored to interrupt, PD and IDL bits are cleared and
idle mode is not entered.
Table 62 shows the state of ports during idle and power-down modes.
Table 62. State of Ports
Mode
Idle
Program Memory
Internal
ALE
PSEN
PORT0
Port Data(1)
Floating
PORT1
PORT2
PORT3
1
1
0
0
1
1
0
0
Port Data
Port Data
Port Data
Port Data
Port Data
Address
Port Data
Port Data
Port Data
Port Data
Port Data
Port Data
Idle
External
Power Down
Power Down
Internal
Port Data(1)
Floating
External
Port 0 can force a 0 level. A "one" will leave port floating.
83
4180E–8051–10/06
ATMEL [ ATMEL ]
