8XC52/54/58
If desired, ALE operation can be disabled by setting
bit 0 of SFR location 8EH. With this bit set, the pin is
weakly pulled high. However, the ALE disable fea-
ture will be suspended during a MOVX or MOVC in-
struction, idle mode, power down mode and ICE
mode. The ALE disable feature will be terminated by
reset. When the ALE disable feature is suspended or
terminated, the ALE pin will no longer be pulled up
weakly. Setting the ALE-disable bit has no affect if
the microcontroller is in external execution mode.
272336–5
e
g
30 pF 10 pF for Crystals
C1, C2
For Ceramic Resonators, contact resonator manufac-
turer.
Figure 3. Oscillator Connections
Throughout the remainder of this data sheet, ALE
will refer to the signal coming out of the ALE/PROG
pin, and the pin will be referred to as the ALE/PROG
pin.
To drive the device from an external clock source,
XTAL1 should be driven, while XTAL2 floats, as
shown in Figure 4. There are no requirements on the
duty cycle of the external clock signal, since the in-
put to the internal clocking circuitry is through a di-
vide-by-two flip-flop, but minimum and maximum
high and low times specified on the data sheet must
be observed.
PSEN: Program Store Enable is the read strobe to
external Program Memory.
When the 8XC5X is executing code from external
Program Memory, PSEN is activated twice each
machine cycle, except that two PSEN activations
are skipped during each access to external Data
Memory.
An external oscillator may encounter as much as a
100 pF load at XTAL1 when it starts up. This is due
to interaction between the amplifier and its feedback
capacitance. Once the external signal meets the V
IL
and V specifications the capacitance will not ex-
EA/V
: External Access enable. EA must be
PP
IH
ceed 20 pF.
strapped to VSS in order to enable the device to
fetch code from external Program Memory locations
0000H to 0FFFFH. Note, however, that if any of the
Lock bits are programmed, EA will be internally
latched on reset.
EA should be strapped to V
executions.
for internal program
CC
This pin also receives the programming supply volt-
age (V ) during EPROM programming.
PP
272336–6
XTAL1: Input to the inverting oscillator amplifier.
Figure 4. External Clock Drive Configuration
XTAL2: Output from the inverting oscillator amplifi-
er.
IDLE MODE
The user’s software can invoke the Idle Mode. When
the microcontroller is in this mode, power consump-
tion is reduced. The Special Function Registers and
the onboard RAM retain their values during Idle, but
the processor stops executing instructions. Idle
Mode will be exited if the chip is reset or if an en-
abled interrupt occurs.
OSCILLATOR CHARACTERISTICS
XTAL1 and XTAL2 are the input and output, respec-
tively, of a inverting amplifier which can be config-
ured for use as an on-chip oscillator, as shown in
Figure 3. Either a quartz crystal or ceramic resonator
may be used. More detailed information concerning
the use of the on-chip oscillator is available in Appli-
cation Note AP-155, ‘‘Oscillators for Microcontrol-
lers’’, Order No. 230659.
5
INTEL [ INTEL ]
