–

–

–

–

8

9

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