at89s8253-24psu ATMEL Corporation, at89s8253-24psu Datasheet - Page 34

• Manufacturer Part Number: at89s8253-24psu
• Description: At89s8253 8-bit Microcontroller With 12k Bytes Flash And 2k Bytes Eeprom
• Manufacturer: ATMEL Corporation

17. Idle Mode
34
AT89S8253
Figure 16-3. Ceramic Resonator Clock Source
To drive the device from an external clock source, XTAL2 should be left unconnected while
XTAL1 is driven, as shown in
Figure 16-4. External Clock Drive Configuration
In idle mode, the CPU puts itself to sleep while all the on-chip peripherals remain active. This
mode is invoked by software. The content of the on-chip RAM and all the special functions 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.
Table 17-1.
Mode
Idle
Idle
Power-down
Power-down
6
5
4
3
2
1
0
Status of External Pins During Idle and Power-down Modes
2
Program Memory
Internal
External
Internal
External
4
6
Figure
8
Ceramic Resonator Clock Input
10
16-4.
Frequency (MHz)
ALE
1
1
0
0
12
14
PSEN
1
1
0
0
16
18
PORT0
Float
Float
Data
Data
20
22
PORT1
Data
Data
Data
Data
24
Address
PORT2
Data
Data
Data
0 pF
5 pF
10 pF
3286K–MICRO–12/06
PORT3
Data
Data
Data
Data