HT12D & HT12E

Multiplexing is the process of transmitting a large number of information over a single line. A digital multiplexer is a combination circuit that selects ‘one digit as information from several sources and transmits the selected information on a single output line. A multiplexer is also called a data selector.

Demultiplexing is the process of talking information from one input and transmitting the same over one of several outputs. A Demultiplexing is a logic circuit that receives information on a single input and transmits the same information over one of several outputs.

A decoder is similar to demultiplexer but without any data input. Most digital systems require the decoding of data. Decoding is necessary in applications such as data demultiplexing, digital display, digital to analog converters etc. In a decoder, the number of output is greater is than number of inputs.

An encoder is similar to multiplexer.

HT12D is a decoder integrated circuit that belongs to 2¹² series of decoders. This series of decoders are mainly used for remote control system applications, like burglar alarm, car door controller, security system etc. It is mainly provided to interface RF and infrared circuits.  They are paired with 2¹² series of encoders. The chosen pair of encoder/decoder should have same number of addresses and data format.

In simple terms, HT12D converts the serial input into parallel outputs. It decodes the serial addresses and data received by, say, an RF receiver, into parallel data and sends them to output data pins. The serial input data is compared with the local addresses three times continuously. The input data code is decoded when no error or unmatched codes are found. A valid transmission in indicated by a high signal at VT pin.

HT12E is an encoder integrated circuit of 2¹² series of encoders. They are paired with 2¹² series of

decoders for use in remote control system applications. It is mainly used in interfacing RF and infrared circuits. The chosen pair of encoder/decoder should have same number of addresses and data format.

Simply put, HT12E converts the parallel inputs into serial output. It encodes the 12 bit parallel data into serial for transmission through an RF transmitter. These 12 bits are divided into 8 address bits and 4 data bits.

 HT12E has a transmission enable pin which is active low. When a trigger signal is received on TE pin, the programmed addresses/data are transmitted together with the header bits via an RF or an infrared transmission medium. HT12E begins a 4-word transmission cycle upon receipt of a transmission enable. This cycle is repeated as long as TE is kept low. As soon as TE returns to high, the encoder output completes its final cycle and then stops