Reduced emi mode – Rainbow Electronics AT89C5122 User Manual
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AT8xC5122/23
4202E–SCR–06/06
Figure 109. Power-down Exit Waveform
Exit from power-down by reset redefines all the SFRs, exit from power-down by external
interrupt does no affect the SFRs.
Exit from power-down by either reset or external 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 shows the state of ports during idle and power-down modes.
Note:
1. Port 0 can force a 0 level. A "one" will leave port floating.
Reduced EMI Mode
The ALE signal is used to demultiplex address and data buses on port 0 when used with
external program or data memory. Nevertheless, during internal code execution, ALE
signal is still generated. In order to reduce EMI, ALE signal can be disabled by setting
AO bit.
The AO bit is located in AUXR register at bit location 0. As soon as AO is set, ALE is no
longer output but remains active during MOVX and MOVC instructions and external
fetches. During ALE disabling, ALE pin is weakly pulled high.
INT1
INT0
XTAL1
Power-down phase
Oscillator restart phase
Active phase
Active phase
Table State of Ports
Mode
Program Memory
ALE
PSEN
P0
P1
P2
P3
P4
P5
Idle
Internal
1
1
Port Data
(1)
Port Data
Port Data
Port Data
Port Data
Port Data
Idle
External
1
1
Floating
Port Data
Address
Port Data
Port Data
Port Data
Power-down
Internal
0
0
Port Dat*
Port Data
Port Data
Port Data
Port Data
Port Data
Power-down
External
0
0
Floating
Port Data
Port Data
Port Data
Port Data
Port Data