4
P/N:PM0591
REV. 0.3, APR. 09, 1999
MX10C805X
RST : Reset input. A high on this pin for two machine
cycles while the oscillator is running resets the device.
The port pins will be driven to their reset condition when
a minimum VIHI voltage is applied whether the oscillator is running or not. An internal pulldown resistor permits a power-on reset with only a capacitor connected
to VCC.
ALE : Address Latch Enable output pulse for latching
the low byte of the address during accesses to external
memory .
In normal operation ALE is emitted at a constant rate of
1/6 the oscillator frequency, and may be used for e xternal timing or clocking purposes. Note, however, that
one ALE pulse is skipped during each access to external Data Memory .
If desired, ALE operation can be disabled by setting bit
5 of SFR location 87H (PCON). With this bit set, the pin
is weakly pulled high. Howe ver, the ALE disab le feature
will be suspended during a MOVX or MO VC instruction,
idle mode, power do wn mode. The ALE disable f eature
will be terminated by reset. When the ALE disable f eature is suspended or terminated, the ALE pin will no
longer be pulled up weakly. Setting the ALE-disable bit
has no affect if the micrcontroller is in external execution mode.
Throughout the remainder of this data sheet, ALE will
refer to the signal coming out of the ALE pin, and the pin
will be referred to as the ALE pin.
PSEN : Progr am Store Enable is the read strobe to external Program Memory.
When the MX10C805X is executing code from e xternal
Program memory, PSEN is activated twice each machine cycle, except that two PSEN activations are
skipped during each access to external Data memory.
EA/VPP : Extrernal Access enable. EA must be str apped
to VSS in order to enable the twiceto fetch code from
external Program Memory locations 0000H to 0FFFFH.
EA will be internally latched on reset.
EA should be strapped to VCC f or internal program executions.
XTAL1 : Input to the inverting oscillator amplifier.
XTAL2 : Output from the inverting oscillator amplifier.
T o drive the de vice from an external clock source, XTAL1
should be driven, while XTAL2 floats, as shown in Figure 4. There are no requirememts on the duty cycle of
the external clock signal, since the input to the internal
clocking circuitry is through a divide-by-two flip-flop, b ut
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 amplifer and its feedback capacitance. Once the e xternal signal meets the VIL and VIH
specifications the capacitance will not exceed 20 pF.
C2
XTAL2
XTAL1
VSS
Figure 3. Oscillator Connections
C1, C2 = 30 pF is equal to or less than 10 pF for Crystal
For Ceramic Resonators,contact resonator manufacture.
C1
N/C
XTAL1
VSS
XTAL2
EXTERNAL
OSCILLATOR
SIGNAL
Figure 4. External Clock Drive Configuration
OSCILLA T OR CHARA CTERISTICS
XT AL1 and XTAL2 are the input and output, respectively ,
of a inverting amplifier which can be configured for use
as an on-chip oscillator, as sho wn in Figure 3. Either a
quartz crystal or ceramic resonator may be used.