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Monday, September 5, 2011

HT12E Encoder for Engineering projects

HT12E Encoder for Engineering projects
  Most of the Engineering projects need the HT12E encoder for remote controlled systems applications.
They are capable of encoding information which consists of N address bits and 12_N data bits. Each address/ data input can be set to one of the two logic states. The programmed addresses/data are transmitted together with the header bits via an RF or an infrared transmission medium upon receipt of a trigger signal. The capability to select a TE trigger on the HT12E or a DATA trigger on the HT12A further enhances the application flexibility of the 212 series of encoders.
Operation The 212 series of encoders begin a 4-word transmission cycle upon receipt of a transmission enable (TE for the HT12E or D8~D11 for the HT12A, active low). This cycle will repeat itself as long as the transmission enable (TE or D8~D11) is held low. Once the transmission enable returns high the encoder output completes its final cycle and then stops as shown in the timing diagram shown above. 
The status of each address/data pin can be individually pre-set to logic _high_ or _low_. If a transmission- enable signal is applied, the encoder scans and transmits the status of the 12 bits of address/ data serially in the order A0 to AD11 for the HT12E encoder and A0 to D11 for the HT12A encoder. During information transmission these bits are transmitted with a preceding synchronization bit. If the trigger signal is not applied, the chip enters the standby mode and consumes a reduced current of less than 1_A for a supply voltage of 5V. Usual applications preset the address pins with individual security codes using DIP switches or PCB wiring, while the data is selected by push buttons or electronic switches. For the HT12E encoders, transmission is enabled by applying a low signal to the TE pin. 
The address pins of the encoder are joined with controller’s port 0. The data pins of the encoder are linked with controllers port P2.0 to P2.3.Once the data and address are set by the controller, the transmission enable pin of the encoder connected with the pin P2.4 of the controller is set to LOW. Thus enabling the transmission, the data is sent to the RF transmitter module , transmitting the signal continuously till the transmission enable pin to set to HIGH.

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