AT89C51RC-24PC View Datasheet(PDF) - Atmel Corporation
Part Name
Description
MFG CO.
'AT89C51RC-24PC' PDF : 36 Pages View PDF
Figure 16-1. Interrupt Sources
0
INT0
1
AT89C51RC
IE0
TF0
0
INT1
IE1
1
TF1
TI
RI
TF2
EXF2
17. Oscillator Characteristics
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 Figure 19-1. Either a quartz crystal or
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 Figure 19-2. There are no
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.
18. 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 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.
19
1920C–MICRO–03/05
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