Hitachi RAS-E10H2 - Page 40

2.
Indoor/Outdoor Interface Ci
rc
ui
t
The interface circuit superimposes an interface signal on the DC 35V line to perform communications
between
indoor
and
outdoor
units
.
This
circuit
consists
of
a
transmitting
circuit
which
super
imposes
an
interface
signal
transmit
from
the
microcomputer
on
the
DC
35V
line
and
a
circuit
which
detects
the
interface signal on the DC 35V line.
Communications are perf
or
Communications are perforCommunications are perf
med alter
nativ
ely transmitting and receiving.
2-1 Communication signal from outdoor microcomputer to indoor microcomputer
.
2-1 Communication signal from outdoor microcomputer to indoor microcomputer.2-1 Communication signal from outdoor microcomputer to indoor microcomputer
At first outdoor microcomputer will send a request signal (SDO) to indoor microcomputer
.
38
KHz
of
carr
ier
signal
is
generated
and
modulated
by
the
request
signal
(SDO)
from
the
outdoo
r
microcomputer
pin
48.
This signal is superimposed to DC 35V line via C801 and L801
.
To
pre
ve
nt
erroneous
reception,
the
outdoor
microcomputer
is
designed
so
that
it
cannot
receiv
e
a
signal while it is outputting a request signal.
The
receiving
circuit
in
the
indoor
unit
consists
of
a
comparator
and
tr
ansistor
.
The
interf
ace
signal
from
the
outdoor
unit
on
the
DC
35V
line
is
supplied
to
C821,
where
DC
components
are
eliminated, and
is
then shaped
b
y the comparator
. T
he shaped signal is detected
by
diode, amplified
by
amp
, and output
to pin 49 of the indoor microcomputer
.
Fig.
2-2
shows
the
waveforms
at
each
component
when
data
is
transferred
from
the
outdoor
microcomputer to the indoor microcomputer
.
2-2 Communication signal from indoor microcomputer to outdoor microcompute
r.
Q801
.
indoor microprocessor
.
This
modulated
I/F
signal
is
then
amplified
and
superimposed
to
DC
35V
line
via
L801
and
C802
of
indoor
interf
ace
circuit.
Fig.
2-3
shows
the
waveforms
at
each
component
when
data
is
transferred
from
outdoor
microcomputer
to indoor microcomputer
.
The circuit operation of the outdoor receiving circuit is same as indoor receiving circuit.
The request signal (SDO) generates by indoor microcomputer is output to pin 50, and amplifies by
I/F signal approx. 38 kHz is generated by comparator
, then modulated by the signal from pin 50 of
Micro Computer
HIC 
TERMINAL
BOARD
(Communications from indoor microcomputer to outdoor microcomputer)
(Communications from outdoor microcomputer to indoor microcomputer)
Fig. 2-1 Indoor / Outdoor interface circuit
CONTROL P.W.B.
MAIN P.W.B.
35V
0V
0V 0V
5V
5V
0V
0V
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