All and more about Sharp PC
-1
500 at http:/lwww.PC-1500.info
2-3. Functions
14
2-3-1. Timer
T
he
t
im
er
is
a 9-bit polynominal counte
r.
The counter
val
ue can be set by t
he
A
MO
or
AM
I instruction
(l
f t
he
CP
U.
Shown
in
"
POLI
NOM
I
NAL
COU
NTER"
is the
li
st of
hexadecimal data
of
counter
wit
h decimal count numbe
r.
TI
1e timer operat
es
continuously at all
tim
es. When the count
er
va
l
ue
reaches I
FFH.
it
iss
u
es
interrupt requ
es
t
rn
t
he
CPU. If IE (Interrupt Enab
le)
nag is active at that point. the
CPU
jump
s to
th
e timer i
nt
errupt processing routine
who
se
high
order b
yte
address
is
re
presented by the contents
of
the address
FFFAH
and low order byte address by t
he
contents
of
the address
FFF
BH
. The ti
mer
has to be
se
t to
OOOH
when it is not
use
d.
Since it counts
in
syn
ch
ronization wi
th th
e
cl
ock
<1>
F, each one cy
cle
of
<1>
F
in
crements the
counter o
ne
step.
Oscillator
'--~D
~
i
v
_
id
_
e
r
~__,
~
<1>
F
Wh
en the 4M Hz crystal osci
llat
or is
in
connectio
n.
th
e timer
is
incremented
at
each
32~1s
ec
.
bcca use
(!>
F
is
3 I .
25k
Hz.
Do
not
sell this PDF !!!
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