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DECODER OPERATION
The LS Series decoder begins by waiting for the DATA_IN line to transition from
low to high. At that point, the decoder will accept the data, check it for errors, and
confirm that the bytes are valid. If the data pass all of the checks, then the data
bits are output on the decoder’s data lines. If any of these checks fail, then the
decoder will ignore the received packet and look for the next one.
The decoder has a built-in debounce circuit to guard against signal cutout. This
is a timer that maintains the current state of the data lines until changed by a
valid packet or until no valid packets are received for 131mS. After 131mS, the
decoder pulls all of the data lines to ground and goes back to sleep. This helps
protect devices attached to the decoder by smoothing out the output response.
Rapid switching resulting from lost packets could cause damage to devices,
such as relays or motors, that may be controlled by the decoder.
This debounce circuit helps in noisy environments and at the range limit of the
link where lost packets and cutouts are more frequent. The drawback is that
there is a 131mS lag time between the end of the transmission and when the
data lines are turned off. This is generally not a problem with manual remote
control applications, but must be taken into account in applications where timing
is critical.
TYPICAL APPLICATIONS
LS Series encoders and decoders would typically be used in remote control
applications to register button presses and activate circuitry in a remote device.
Figure 4 shows an example application circuit.
An SPDT switch is used in both circuits to set the baud rate. This switch will pull
the BAUD_SEL line to either ground or V
CC
for selection of one of the baud rates
listed in the Pin Descriptions section. The baud rate on both sides must match in
order for the encoder and decoder to correctly operate.
Two pushbutton switches are connected to the data lines on the encoder. Since
none of the data lines have internal pull resistors, external resistors are used to
pull the data lines to ground when not in use. Without these resistors, the state
of the data lines can not be guaranteed and performance may not be predictable.
In this example, only two data lines are used, so the other two are tied directly to
ground. With this circuit, pressing either of the buttons will cause the data line to
go high and initiate a transmission.
On the decoder side, a piezoelectric buzzer is attached directly to the D1 line.
When the button connected to the D1 line on the encoder is pressed, the buzzer
will sound. The D0 line is connected to a relay through a transistor buffer. The
decoder can output 25mA, which is sufficient to drive small relays, but may not
work for larger coils. The transistor is used to provide the higher current and
voltage required to activate a larger relay. With this circuit, when the D0 line goes
high, it will turn on the transistor, which will energize the relay and connect the
terminals.
PIN DESCRIPTIONS
V
CC
This is the positive power supply.
DATA_OUT
The encoder will output a serial data stream on this line.
DATA_IN
The decoder will monitor this line for data.
SEL_BAUD
This line is used to select the baud
rate of the serial data stream. The
state of the line allows the selection of
one of two possible baud rates, as
shown in the adjacent table.
GND
These lines are connected to ground.
Data Lines
The LS Series has three data lines, D0 through D3. When any of these lines
goes high on the encoder, their states are recorded, encoded for transmission,
and then reproduced on the outputs of the decoder.
PRODUCTION CONSIDERATIONS
LS Series encoders and decoders are implemented in an industry standard 8-
Lead Plastic Dual In-Line Package (8-PDIP). The package and layout
dimensions are shown on Page 1. These components are leaded through-hole
parts and may be hand- or wave-soldered.
THEORY OF OPERATION
The Linx LS Series encoder and decoder are designed to register button presses
or contact closures. When a pin goes high on the encoder, a signal is sent to
make a corresponding pin go high on the decoder. The outputs of the decoder
can then be used to activate almost anything, from driving a LED or buzzer to
activating digital circuitry.
The LS Series does not require any programming or addressing and its simplicity
makes it a good choice for basic remote control devices that are designed to turn
something on and off.
ENCODER OPERATION
Upon power-up, the encoder enters sleep mode. As soon as one of the data lines
goes high, it will wake up and begin the transmit process.
First, the encoder will record the state of the data lines, encode for error
correction, and assemble the packet. It will then output the packet on the
DATA_OUT line. The encoder will repeat the transmission process for as long as
one of the data lines is high, otherwise it will go back to sleep. It will update the
state of the data lines with each packet, and it will finish the current transmission
even if all of the lines are pulled to ground.
SEL_BAUD Baud Rate (bps)
0 2,400
1 9,600
Table 2: Baud Rate Selection Table
