Linx Technologies LICAL-TRC-MT - Manual (Page 17)

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Typical Applications
The MT Series transcoder is ideal for replicating button presses for remote
control applications. An example application circuit is shown in Figure 24.
SPDT switches are used to select the baud rate and set the latch mode.
These can be tied directly to supply or ground if they will not change.
The TR_PDN line can be connected to the PDN line of a transceiver or it
can be left floating.
SER_IO can be connected to a microprocessor or a PC to program the
transcoder through the serial command set or to record the transmitter
identity. Application Note AN-00157 has sample code.
An LED indicator is attached to the MODE_IND line to provide visual
feedback to the user that an operation is taking place. This line can
source a maximum of 25mA, so the limiting resistor may not be needed,
depending on the LED chosen and the brightness desired.
The CONFIRM line is connected to an LED to indicate that the remote
device successfully received the command.
The CRT/LRN and ENC_SEL lines are connected to buttons that pull the
lines high when pressed. 100k
Ω resistors are used to pull the lines to
ground when the buttons are released.
The TR_DATA line is connected directly to the data line of the transceiver.
VCC
D6
D7
CRT/LRN
ENC_SEL
SER_IO
CONFIRM
TR_PDN
TR_SEL
TR_DATA GND
D5
D4
D3
LATCH
SEL_BAUD
MODE_IND
D2
D1
D0
1
2
3
4
5
6
7
8
9
10 11
12
13
14
15
16
17
18
19
20 LICAL-TRC-MT
To Transceiver
2.2k 10k
To Processor or PC
To Transceiver
To Transceiver
100k
100k
100k
VCC
VCC
100k
VCC
VCC
VCC
VCC
VCC
VCC
Figure 24: MT Series Transcoder Application Circuit
Data Lines D0 through D7 can be individually set up as either inputs or
outputs. In this example, D4 and D5 have buttons connected to them,
so they are set up as inputs, and D0 and D6 are set up as outputs. D0
is connected directly to a piezoelectric buzzer. Line D6 activates a relay
through a transistor buffer when it goes high. A buffer like this may be
needed if the load requires more than 25mA of current or a higher voltage
source to activate. The transcoder turns on the transistor, which can be
selected to provide the appropriate drive levels to activate the relay.
Operation with the MS Series
The MT Series transcoders are fully compatible with the MS Series
encoders and decoders. Tying the ENC_SEL line high makes the
transcoder operate just like an MS Series encoder. Tying this line low
enables it to become an MS decoder or a transcoder, depending on how it
is set-up. This is described in detail in the Transcoder Operation section.
There are two important issues of note when using the transcoders with
the MS Series. First, only two of the MS baud rates are supported by the
MT; 9,600bps and 28,800bps. Second, the MS Series does not respond to
the advanced features of the MT, like the custom data and Targeted Device
Addressing. The main advantage offered by the MT over the MS is the
serial interface. This allows a number of advanced options to be realized.
Some other advantages are:
• More users (60 vs. 40)
• Automatic confirmation
• The lower duty cycles (25% vs. 50%) of the MT Series allows for greater
range in countries like the United States that average transmitter output
power over time
• The serial output on every packet instead of just once per receive
session
• Allows existing receive stations using the MS Series decoder to be
upgraded to take advantage of the advanced features without having to
upgrade existing transmitter stations based on the MS Series encoder
• Mixed MS / MT-based systems that allow cost savings for units that only
require unidirectional operation while other units require bidirectional
operation