Filter
Top Products
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.
DIAGRAM OF 8048
CLOCK
UTILITIES
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
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
CLOCK
OUT
ON
TO
ALE
51
52
--"f---+--+-'
sa
54
55
~~f--~--+--~--~-,
51
52
~
~~----.,----~
PROG
2-10
53 54
55