HT12D

General Description:
The 212 decoders are a series of CMOS LSIs for remote control system applications. They are paired with Holtek s212 series of encoders (refer to the encoder/de- coder cross reference table). For proper operation, a pair of encoder/decoder with the same number of ad- dresses and data format should be chosen.
The decoders receive serial addresses and data from a programmed 212 series of encoders that are transmitted by a carrier using an RF or an IR transmission medium. They compare the serial input data three times continu-
ously with their local addresses. If no error or un- matched codes are found, the input data codes are decoded and then transferred to the output pins. The VT pin also goes high to indicate a valid transmission. The 212 series of decoders are capable of decoding informations that consist of N bits of address and 12N bits of data. Of this series, the HT12D is arranged to pro- vide 8 address bits and 4 data bits, and HT12F is used to decode 12 bits of address information.
BLOCK DIAGRAM:

Functional Description:
Operation The 212 series of decoders provides various combina- tions of addresses and data pins in different packages so as to pair with the 212 series of encoders.
The decoders receive data that are transmitted by an encoder and interpret the first N bits of code period as addresses and the last 12N bits as data, where N is the address code number. A signal on the DIN pin activates the oscillator which in turn decodes the incoming ad- dress and data. The decoders will then check the re- ceived address three times continuously. If the received address codes all match the contents of the decoder s local address, the 12N bits of data are decoded to acti- vate the output pins and the VT pin is set high to indicate a valid transmission. This will last unless the address code is incorrect or no signal is received.
The output of the VT pin is high only when the transmis- sion is valid. Otherwise it is always low.

Pin assignment:

A0~A7 : Input pins for address A0~A7 setting These pins can be externally set to VSS or left open.
D8~D11: Output data pins, power-on state is low.
DIN: Serial data input pin
VT: Valid transmission, active high
OSC1: Oscillator input pin
OSC2: Oscillator output pin
VSS: Negative power supply, ground
VDD: Positive power supply