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Basic Information
Functional Description
Question 1
What makes the HT45R22E especially suitable for learning type remote controller applications? What MCU resources are required?
Answer
The learning type remote controller hardware requires an EEPROM to store the learned data, and also an amplifier to handle the data waveform. The HT45R22E includes two operational amplifiers, one comparator, 1K byte of EEPROM and up to 22 I/O pins, all which increase the cost effectiveness of the device making it an ideal choice for learning type remote controller applications.
Question 2
What is the purpose of the EEPROM in the HT45R22E learning type remote control MCU? What is the capacity of the EEPROM?
Answer
The EEPROM capacity of the HT45R22E is 1024 x 8 bits and it is used to store the learned data.
Question 3
What are the OPA and comparator used for in the HT45R22E learning type remote control MCU?
Answer
The OPA in the HT45R22E is used to amplify the data code learned from the remote controller. The comparator is used to process the signal after amplification.
Question 4
What is the IRC for in the HT45R22E learning type remote control MCU?
Answer
The IRC is a fully internal system oscillator which will increase device cost effectiveness.
Question 5
What is accuracy of the IRC in the HT45R22E? How does it affect learning type remote control applications?
Answer
The HT45R22E includes a high accuracy internal IRC, which at a VDD of 3V will have a tolerance within ±2% at room temperature. For the reason that the system frequency is the basis behind learning code counting, the frequency tolerance will affect the accuracy of the learned code and may result in a failed learning operation or erroneous operation. To decrease learning failures from happening, the actual operating frequency, in coded format, can be placed into the last address of the Program Memory. The application program can then be used to compensate for system frequency errors. For detailed specifications please refer to the application note.
Question 6
How does the HT45R22E learn remote control signals?
Answer
The HT45R22E will completely record all of the received data of the remote controller being learned. The learning process is subdivided into two parts, carrier learning and waveform learning. Carrier learning uses the input capture function of the timer to obtain the length of both high and low pulses. The timer function is then used to obtain the remote waveform time which contains the carrier and also the blank time o f the waveform. For detailed program codes please refer to the relevant application note.
Question 7
Do variations in the HT45R22E system frequency influence the remote controller learned signals?
Answer
The carrier output signal of the remote controller is based on the system frequency whose variations could lead to remote controller transmission signal errors. The HT45R22E provides three oscillators, an IRC, ERC and Crystal. Users should select a suitable system oscillator according to the accuracy requirements of their applications.
Question 8
How does the HT45R22E transmit HT6221A codes?
Answer
The HT45R22E is not equipped with a carrier generation module and output pin. The carrier and output of the HT6221A can be implemented by a timer or instruction clock with I/O software programming.
Question 9
What is the maximum number of keys the HT45R22E can implement?
Answer
The length of different coding types varies, so the data capacity for the 1K byte EEPROM in the HT45R22E is decided by the actual coding format and data processing method.
Question 10
What is the maximum number of keys the HT45R22E can implement?
Answer
For the conditions of not adding a diode, if the number of I/Os is equal to N, then (N-1)/2+N scanning keys can be implemented. The HT45R22E provides 22 I/O pins. With the exception of the OPA/CP pins for signal amplifying, compensation and IR transmission functions, there are still 18 pins remaining. This means that 18 x (18-1)/2+18=171 scanning keys can be implemented. For detailed circuit and scanning principles please refer to the application notes.
Application Description
Points to Note
Question 1
When using the HIRC, if the I/O pin which is shared with OSC1 is to be used as an AC zero crossing detector, will there be any influence on the HIRC oscillation frequency? If yes, which MCUs will be affected and how can this problem be resolved?? Answer
If the HIRC is used and if the I/O pin which is shared with OSC1 is used as an AC zero crossing detector pin, the HIRC oscillation frequency will be influenced.
The affected MCUs are:
All MCUs whose I/O pin is pin-shared with OSC1 (including the enhanced OTP type MCU and Flash type MCU etc.)
How to resolve this issue:
1. Avoid using the I/O pin that is shared with OSC1 as AC zero crossing detector pin.
2. If the problem can still not be resolved, add external circuitry to ensure that the voltage applied on the OSC1 pin remains withing the range of VDD and VSS.
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