Datasheet

7764A–8051–11/07

1.3.1 Test conditions

It is recommended to monitor the clock on XTAL2 pin.

Special care must be taken when measuring XTAL1 signal. A high impedance probe must be

used to avoid any distorsion of the signal.

Test condition: probe’s impedance > 1 MOhm

This means that oscilloscope’s active probes are prohibited due to their weak impedance (usu-

ally around 100KOhm)

1.3.2 Relationship between oscillator and ALE frequencies

Output pulse for latching the low byte of the address during an access to external memory. In

normal operation, ALE is emitted at a constant rate of the oscillator frequency and can be used

for external timing or clocking.

Note that one ALE pulse is skipped during each access to external data memory.

ALE can be disabled by setting SFR’s AUXR.0 bit. When this bit is set, ALE will be inactive dur-

ing internal fetches.

XTAL1

XTAL2

Microcontroller

High impedance probe

MCU’s Clock mode ALE frequency

X1 mode Freq(ale) = Freq(osc )/6

X2 mode Freq(ale) = Freq(osc )/3