AT89S8253 Atmel Corporation, AT89S8253 Datasheet - Page 35

• Manufacturer Part Number: AT89S8253
• Manufacturer: Atmel Corporation

Specifications of AT89S8253

• Flash (kbytes): 12 Kbytes
• Max. Operating Frequency: 24 MHz
• Cpu: 8051-12C
• Max I/o Pins: 32
• Spi: 1
• Uart: 1
• Sram (kbytes): 0.25
• Eeprom (bytes): 2048
• Operating Voltage (vcc): 2.7 to 5.5
• Timers: 3
• Isp: SPI
• Watchdog: Yes

17. Idle Mode
3286P–MICRO–3/10
Figure 16-5. Ceramic Resonator Clock Source (B)
To drive the device from an external clock source, XTAL2 should be left unconnected while
XTAL1 is driven, as shown in
Figure 16-6. 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.
7
6
5
4
3
2
1
0
0
4
Ceramic Resonator Clock Input
Figure
8
16-6.
Frequency (MHz)
12
16
20
AT89S8253
C2=0pF
C2=5pF
C2=10pF
R1=4MΩ
24
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