Linx Technologies LICAL-DEC-MS001 - Manual (Page 7)

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Encoder Comparison Table
Manual Address Encoders
Advantages
High number of button inputs
Disadvantages
Low-security fixed code
Confusing manual addressing
Low number of addresses
PWM data output
High security vulnerabilities
"Rolling Code" Encoders
Advantages
Highly secure
Eliminates manual address settings
Disadvantages
Low number of button inputs
Encoder and decoder can become unsynchronized
Difficult or impossible to create relationships
Security vulnerabilities
Linx Encoders
Advantages
High number of button inputs
Highly unique (MS)
Highest security available on the market (HS)
Eliminates manual address settings
Allows for associative relationships
Cannot unsynchronize
Serial data output
Encoder ID is output by the decoder
Latched or momentary outputs (MS)
External transmitter and receiver control lines
Disadvantages
Slightly higher cost for some basic applications
Security vulnerabilities (MS only)
Figure 8: Encoder Comparison Table
Decoder Operation
When the decoder first powers up, it sets the baud rate and checks the
state of the RX_CNTL line. If this line is pulled high, then the decoder goes
into Receiver Control Mode. If the line is low, it goes to sleep until a rising
edge (low to high transition) on the DATA_IN line puts it into Receive Mode
or a high signal on the LEARN line puts it into Learn Mode.
Receive Mode
When a rising edge is seen on the DATA_IN line, the decoder enters
Receive Mode. The decoder looks for a valid packet, meaning that there
are no errors and that the received Address matches one that is saved in
memory. If there is a match, then the decoder reproduces the states of
the encoder’s data lines on its own data lines. It also outputs the ID of the
encoder once, on reception of the first valid packet. It then looks for the
next valid data packet. If, at any time, an error or an unknown Address is
detected, the decoder ignores the packet and looks for the next one.
If the timer runs out, then the decoder goes back to sleep. This time
is dependent upon the baud rate selected by the user. It is 131ms for
2,400bps and 9,600bps, and 65ms for 19,200bps and 28,800bps.
Learn Mode
In order for the decoder to accept transmissions from an encoder, it must
first learn the encoder’s Address. This is done by taking the LEARN line
high to place the decoder into Learn Mode. The MODE_IND line starts
switching, allowing for connection of an LED to provide visual indication
that the decoder is ready to accept a new Address. This continues until the
LEARN line goes high again, or until a time-out after 17 seconds.
The decoder looks for a valid transmission from an MS Series encoder. It
can store up to 40 Addresses in its memory. When the 40th encoder is
learned, the decoder flashes the MODE_IND line five times as an indication
that the memory is full. The next address learned overwrites the first
address in memory. The memory retains all of the learned Addresses if
power is removed.
If the LEARN line is held high for ten seconds, then the decoder erases all
of the stored Addresses from memory. The MODE_IND line is high for as
long as the LEARN line is high, but after the ten seconds it goes low. Once
the LEARN line is pulled low again, the MODE_IND line goes high for two
seconds to indicate that the memory has been cleared.
Baud Rate Selection
SEL_BAUD0 and SEL_BAUD1 are used to select the baud rate of the
serial data stream. The state of the lines allows the selection of one of four
possible baud rates, as shown in Figure 9.
The baud rate must be set before power up. The encoder will not recognize
a change in the baud rate setting after it is on.
Baud Rate Selection Table
SEL_BAUD1 SEL_BAUD0 Baud Rate (bps)
0 0 2,400
0 1 9,600
1 0 19,200
1 1 28,800
Figure 9: Baud Rate Selection Table