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Basic Information
Question 1
What are the main differences between the HT12A/HT12E devices in the
212 series of encoders?
Answer
The address/data pin format of the HT12A and HT12E devices are the same. However, the HT12A address/data have a 38KHz infra-red carrier wave output, making the device suitable for infra-red remote control applications. The HT12E does not have this infra-red carrier wave output.
Question 2
What is the code transmission order for the HT12E?
Answer
The HT12E can be used to encode remote control signals. After 8-bits of address and 4-bits of data are setup and the /TE pin is pulled low, DOUT will then start to output 4 words of data. After this, if /TE has returned high, then DOUT will cease transmission of the signal. Note that if the /TE signal is removed during a signal transmission the signal will still continue transmission until finished.
At this time the order is shown in Diagram 1 – see attached document 1.
 [document 1]
Each word format is shown in Diagram 2 – see attached document 2.
 [document 2]
There signal is as follows: a 12-bit header code, a 1/3 bit sync. period, the address signal and finally the data signal.
Application Description
Question 1
How to match the oscillating frequencies of the 212 encoders and decoders?
Answer
For 212 series, the oscillating realations between encoders and decoders are :
fosc (HT12D/HT12F decoder) = 50 fosc (HT12E encoder)
fosc (HT12D/HT12F decoder) = 1/3 fosc (HT12A encoder)
If the HT12E is used as encoder, a typical 3kHz oscillating frequency is recommended. The decoder device can be either HT12F or HT12D whose decoder oscillating frequency is typically 50 times that of encoders, namely 150kHz. Take the following steps to find the corresponding resistor values. In the Oscillator Frequency/Supply Voltage graph in the HT12E datasheet, take 5V application for example and the tlypical 3kHz oscillating frequency, a 1.0Mohm resistor is therefore selected. In the Oscillator Frequency/Supply Voltage graph in the HT12D/HT12F datasheet, take 5V and the 150kHz and the resistor will be 51Kohm.
If the HT12A is used as encoder, a 455kHz resonator is recommended. The decoder device can be either HT12E or HT12D whose decoder oscillating frequency is 1/3 that of encoders, namely 152kHz. Take the following steps to find the corresponding resistor values. In the Oscillator Frequency/Supply Voltage graph in the HT12D/HT12F datasheet, take 5V and the 152kHz and the resistor will be around 51Kohm.
Note that user can choose other resistor values as long as the frequency relation is kept and the decoder frequency is under 300kHz, otherwise it might result in decoding failure.
Question 2
How to use the two-state Address pins of the 212 series?
Answer
The 212 series Encoder/Decoder address lines have internal NMOS transmission gate structures. When used, they are tied to either VSS or
VDD/floating. When the line is connected to VSS, Dout will generate a 0 waveform, when the line is connected to
VDD/floating, Dout will generate a 1 waveform.
Question 3
How to use the Holtek MCU to implement the remote decoder function?
Answer
Please refer to the relevant example code in "Application
Notes" under the "Technical Support" section of our company web site.
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