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11
Deccoder Operation
When the decoder first powers up, it will set the baud rate and check the
state of the RX_CNTL line. If this line is pulled high, then the decoder will go
into Receiver Control Mode. If the line is low, it will go 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 will begin by looking for a valid packet,
meaning that there are no errors and that the received Code Word matches
one that is saved in memory. If there is a match, then the decoder will
reproduce the states of the encoder’s data lines on its own data lines. It
will also output the ID of the encoder once, on reception of the first valid
packet. It will then look for the next valid data packet. If, at any time, an
error or an unknown Code Word is detected, then the decoder will ignore
the packet and look for the next one.
If the timer runs out, then the decoder will go 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 Code Word. This is done by taking the LEARN
line high to place the decoder into Learn Mode. Once in Learn Mode, the
MODE_IND line will start switching, allowing for connection of a LED to
provide visual indication that the decoder is ready to accept a new Code
Word. This will continue until the LEARN line goes high again, or until a
time-out after 17 seconds.
The decoder will look for a valid transmission from an MS Series encoder.
It can store up to forty Code Words in its memory. If a new encoder is
learned while the memory is full, then the decoder will write the new word
over the first word in memory. The decoder will flash the MODE_IND line
five times as an indication that the memory is full and the next code learned
will overwrite the first. The memory will retain all of the learned Code Words
if power is removed.