Linx Technologies LICAL-DEC-HS001 - Manual (Page 10)

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Decoder Learn Mode
Learn Mode serves several functions in the HS decoder. First, it provides
the access point for other modes, such as Send Copy, Create Key, and
Clear Memory. It also enables the decoder to learn the Control Permissions
for an encoder. One of the most innovative features of the HS Series
is its ability to establish a unique user identity and profile for the device
containing the encoder. In other products, all encoded transmissions are
either recognized or denied based on the address. In cases where encoder
and decoder addresses match, the state of all data lines is recognized and
output. The HS Series uniquely allows a user or manufacturer to define
which encoder inputs are acknowledged by each decoder.
Consider this practical example: a three door garage houses Dad’s
Corvette, Mom’s Mercedes, and Son’s Yugo. With most competitive
products, any user’s keyfob could open any garage door as long as the
addresses match. In a Linx HS-based system, the keyfobs could easily be
configured to open only certain doors (guess which one Son gets to open!)
The decoder is placed into Learn Mode by pulling the LEARN line high
and then taking it low within ten seconds. The decoder begins toggling the
MODE_IND line to indicate that the decoder is ready to learn the Control
Permissions for a specific encoder. On the encoder end, simply activate
each data line that it should be allowed to access and the decoder records
the lines that were activated as the Control Permissions. Pull the LEARN
line high again or let the decoder timeout after 17 seconds, after which it
automatically exits Learn Mode and returns to sleep.
The decoder can store up to 15 encoder IDs in memory. When the 15th
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. This must be clearly conveyed to the end
user, since system users’ access would be affected by the overwrites. The
memory retains all of the learned encoders if power is removed.
If the LEARN line is held high for ten seconds, the decoder erases all of the
saved User Data from memory. The MODE_IND line is high for as long as
the LEARN line is high, but after 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.
If the SEND_COPY line is high when the LEARN line goes high, the
decoder enters Send Copy Mode. Once in this mode, the state of the
LEARN line is not checked again, so it can be held high or pulled to
ground, whichever is more convenient for the application.
If the CREATE_KEY line is high when the LEARN line goes high, the
decoder enters Create Key Mode.
Decoder TX ID
Upon receipt of the first valid packet, the decoder outputs a binary number
on the KEY_OUT line that corresponds to one of the learned transmitters.
It outputs the number only once, as soon as the first packet is accepted.
An encoder’s key, a 40-bit counter, and permissions are stored in one of
15 memory locations within the decoder. The decoder is able to output
an 8-bit binary number that corresponds to the memory location of the
encoder’s information. The first encoder that is learned is assigned 1, the
second is assigned 2 and so on. Once assigned, it is an easy task for a
software program to read that number and associate it with a particular
encoder. This makes applications such as logging access attempts simple.
The ID is output asynchronously as an eight-bit binary number at the baud
rate selected by the SEL_BAUD line. For example, if the SEL_BAUD line is
grounded and the first encoder that the decoder learned sends a signal,
then once the first packet is received, the decoder outputs ‘0000 0001’
(binary 1) at 2,400bps on the KEY_OUT line.
Application Note AN-00156 shows an example program that reads this
number and displays it on an LCD screen. The code is written in C and is
well documented so that it can be easily modified for a specific application.
The code and include files can be downloaded as a .zip file from the Linx
website.