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2. Indoor/Outdoor Interface Circuit
@ The interface circuit superimposes an interface signal on the 39V DC line supplied from the outdoor unit to perform
communications between indoor and outdoor units. This circuit consists of a transmiting circuit which
superimposes an interface signal transmit from the micro computer on the 39V DC line and a transmiting circuit
which detects the interface signal on the 39V DC line and outputs it to the micro computer.
® Communications are performed by mutually transmiting and receiving the 4-frame outdoor request signal one
frame of which consists of a leader of approx.
100 ms., start bit, 8-bit data and stop bit and the command signal
with the same format transmit from the indoor unit.
@ From outdoor microcomputer to indoor microcomputer
The request signal output from microcomputer pin @ is input to the transmitting circuit. The transmitting circuit
outputs an approx. 38-kHz high-frequency signal via pin @ and continues the output intermittently according to the
request signal. This high-frequency signal is amplified by a transistor, superimposed on the DC 39V line via C801
and L701, and supplied to the indoor unit.
To prevent erroneous reception, the outdoor microcomputer is designed so that it cannot receive a signal while it is
outputting a request signal,
The receiving circuit in the indoor unit consists of a comparator and transistor. The interface signal from the
outdoor unit on the DC 39V line is supplied to C811, where DC components are eliminated, and is then shaped by
the comparator. The shaped signal is detected by diode, amplified by amp, and supplied to receiving input (9 of the
indoor microcomputer.
Fig. 2-2 shows the voltages at each component when data is transferred from the outdoor microcomputer to the
indoor microcomputer.
@ Indoor micro computer to outdoor micro computer
The communications from the indoor micro computer to the outdoor micro computer are the same.
Fig. 2-3 shows
the voltages and waveforms at each circuit.
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