80C52 Datasheet, PDF (5/23 Pages) Intel Corporation – CHMOS SINGLE-CHIP 8-BIT MICROCONTROLLER

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
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
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
EA V_PP External Access enable EA must be
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_CC for internal program
executions
This pin also receives the programming supply volt-
age (V_PP) during EPROM programming
XTAL1 Input to the inverting oscillator amplifier
XTAL2 Output from the inverting oscillator amplifi-
er
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
272336 – 5
C1 C2 e 30 pF g10 pF for Crystals
For Ceramic Resonators contact resonator manufac-
turer
Figure 3 Oscillator Connections
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
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_IH specifications the capacitance will not ex-
ceed 20 pF
272336 – 6
Figure 4 External Clock Drive Configuration
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
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