SINGLE COMPONENT SYSTEM

tor may be used in place of the crystal. With an inductor the oscillator frequency can be approximately 3 to 5 MHz. For higher speed operation a crystal should be used. An externally generated clock may also be applied to X1-X2 as the frequency source. See the data sheet for more information.

State Counter

The output of the oscillator is divided by 3 in the State Counter to create a clock which defines the state times of the machine (ClK). ClK can be made available on the external pin TO by executing an ENTO ClK instruction. The output of ClK on TO is disabled by Reset of the processor.

Cycle Counter

ClK is then divided by 5 in the Cycle Counter to provide a clock which defines a machine cycle conSisting of 5 machine states. This clock is called Address latch Enable (ALE) because of its function in MCS-48 systems with external memory. It is provided continu- ously on the ALE output pin.

2.1.12 Reset

The reset input provides a means for initializa- tion for the processor. This Schmitt-trigger input has an internal pullup resistor which in combination with an external 1 ~fd capacitor provides an internal reset pulse of sufficient length to guarantee all circuitry is reset. If the

DIAGRAM OF 8048 CLOCK UTILITIES

INSTRUCTION CYCLE

 

 

.

2.5 .usee CYCLE

 

.

1 S5

SI

S2

53 1 54 1 S5

SI

I

INPUT

DECODE

EXECUTION

INPUT

INST.

 

 

 

 

OUTPUT ADDRESS

INC. PC

OUTPUT ADDRE55

I

i

 

I

I

~

MCS-48™ CYCLE TIMING

51

52

sa

54

55

51

52

53

54

55

CLOCK OUT

ON TO

ALE --"f---+--+-'

~~f--~--+--~--~-,

~

~~----

.,----~

PROG

 

 

2-10

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Image 37
Intel mcs-48 manual ALE --f---+--+