at89c51rc-33pc ATMEL Corporation, at89c51rc-33pc Datasheet - Page 19

• Manufacturer Part Number: at89c51rc-33pc
• Description: 8-bit Microcontroller With 32k Bytes Flash
• Manufacturer: ATMEL Corporation

17. Oscillator Characteristics
18. Idle Mode
1920C–MICRO–03/05
Figure 16-1. Interrupt Sources
XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier that can be
configured for use as an on-chip oscillator, as shown in
ceramic resonator may be used. To drive the device from an external clock source, XTAL2
should be left unconnected while XTAL1 is driven, as shown in
requirements on the duty cycle of the external clock signal, since the input to the internal clock-
ing circuitry is through a divide-by-two flip-flop, but minimum and maximum voltage high and low
time specifications must be observed.
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 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.
EXF2
INT0
INT1
TF0
TF1
TF2
RI
TI
0
1
0
1
Figure
IE0
IE1
19-1. Either a quartz crystal or
Figure
AT89C51RC
19-2. There are no
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