Linx Technologies LICAL-EDC-DS - Manual (Page 6)

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Initial Operation
On power-up, the E/D_SEL line is tested to determine if the DS operates as
an encoder or a decoder. If the line is high, the DS enters Encoder Mode. If
low, it enters Decoder Mode. This is checked once on power-up. Once the
operating mode is selected, the data-line direction is set. In either mode a
rising edge on the TE/DIN line wakes the device from low-power sleep.
Encoder Mode
Once the DS enters Encoder Mode, it tests the state of the TE line. If it
is high, the P_SEL line is checked to determine which protocol to use.
Then the encoder records the states of the Data and Address lines and
assembles a packet. When the Holtek
® protocol is selected, the DS
outputs the packet on the DOUT line three times. With the Serial protocol,
it sends two packets, checking the states of the data lines each time. The
second packet is the logical inversion of the first packet, ensuring a 50%
duty cycle, which is an advantage for FCC testing. The DS then checks the
state of the TE line again. It repeats this process for as long as the TE line is
high. Once it goes low, the DS goes to sleep until TE is pulled high.
Decoder Mode
When the DS enters Decoder Mode, it checks the state of the DIN line. If
it is high, the P_SEL line is checked to set which protocol is used and the
decoder receives the data. It compares the address in the received packet
to its local address lines. If they match, the data is stored and a second
packet is received. With the Holtek
® protocol, the decoder compares the
two packets. If they match, the received data bits are output on the data
lines and the VT line is pulled high. This protocol compares each packet
with the previous one looking for a match. The serial protocol requires
two matching packets for initial activation, then updates the lines on each
subsequent packet. The DS then looks for the next packet on the DIN line.
With the Holtek ® protocol, once no valid data is received (there is a
mismatch of address, data, or bit timings), the Data and VT lines are pulled
low and the DS goes to sleep until DIN is pulled high. The Serial protocol
holds the output states until a 130ms timer runs out.
The Holtek ® protocol compares two packets and, if they match, sets the
outputs. If a data line is toggled during a transmission (D1 is activated while
D0 is already active) then the received packet does not match the previous
packet and the output lines are pulled low until the next packet arrives. This
causes all of the outputs to briefly cut out when a line is toggled. The serial
protocol uses a timer to prevent this cut out.
Theory of Operation
The DS Series is a remote control encoder and decoder that offers two
protocols in one part based on the state of the P_SEL line. The first
protocol operates with the Holtek
® HT640 encoder and HT658 decoder.
The second is a serial protocol that offers more noise immunity and faster
response time while keeping the simple addressing. The DS can operate
as either an encoder or decoder based on the state of the E/D_SEL line. It
does not operate as both simultaneously.
When set as an encoder it monitors the state of the TE line. When the line
is high the DS records the states of the data and address lines, assembles
them into a packet and outputs the packet three times. The data lines can
be connected to switches or contacts. The address lines can be set with
DIP switches or cut traces on a PCB.
When set as a decoder the DS receives packets and validates them. The
validation includes checking the bit timings and comparing the received
address to the local address line settings. Two matching packets must be
received consecutively. If the timings are good and the addresses match,
the DS sets its data lines to match the received states. These lines can be
connected to the application circuitry to be controlled.
When the TE/DIN line is low, the DS goes into a low power sleep mode.
Setting the Address
The DS Series has ten address lines. This allows the formation of up to
1,022 (2
10 – 2) unique transmitter-receiver relationships.
These lines may be hardwired or configured via a microprocessor, DIP
switch or jumpers. The receiver’s address line states must match the
transmitter’s exactly for a transmission to be recognized. If the addresses
do not match, then the decoder takes no action.
Note: The input lines on the DS are not tri-state. They must be pulled
high or low and cannot be left floating. This is a key difference between
the DS and the Holtek
® parts.
Note: The DS decoder rejects packets with addresses set to all high
or all low. At least one address line must be different from the rest. The
encoder does transmit all addresses, but the decoder rejects packets
with all address lines set the same.