AT89LS51-16PI View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
AT89LS51-16PI
Atmel Corporation
'AT89LS51-16PI' PDF : 32 Pages View PDF
Figure 11-2. External Clock Drive Configuration
NC
XTAL2
EXTERNAL
OSCILLATOR
SIGNAL
XTAL1
GND
AT89LS51
12. Idle Mode
In idle mode, the CPU puts itself to sleep while all the on-chip peripherals remain active. The
mode is invoked by software. The content of the on-chip RAM and all the special function regis-
ters remain unchanged during this mode. The idle mode can be terminated by any enabled
interrupt or by a hardware reset.
Note that when idle mode is terminated by a hardware reset, the device normally resumes pro-
gram execution from where it left off, up to two machine cycles before the internal reset
algorithm takes control. On-chip hardware inhibits access to internal RAM in this event, but
access to the port pins is not inhibited. To eliminate the possibility of an unexpected write to a
port pin when idle mode is terminated by a reset, the instruction following the one that invokes
idle mode should not write to a port pin or to external memory.
13. Power-down Mode
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 mode can be initiated
either by a hardware reset or by activation of an enabled external interrupt (INT0 or INT1). Reset
redefines the SFRs but does not change the on-chip RAM. The reset should not be activated
before VCC is restored to its normal operating level and must be held active long enough to allow
the oscillator to restart and stabilize.
Table 13-1. Status of External Pins During Idle and Power-down Modes
Mode
Program Memory ALE PSEN PORT0 PORT1 PORT2
Idle
Internal
1
1
Data
Data
Data
Idle
External
1
1
Float
Data Address
Power-down Internal
0
0
Data
Data
Data
Power-down External
0
0
Float
Data
Data
PORT3
Data
Data
Data
Data
13
3053B–MICRO–3/05
Share Link: 