Using the HT66F016L and the HT66F50 to Implement Remote Encoding and Decoding

Transcription

1 Using the HT66F016L and the HT66F50 to Implement Remote Encoding and Decoding D/N:AN0327E Introduction This application note describes how to implement a 4 3 Key NEC remote encoding Demo Board using the HT66F016L and an NEC remote decoding Demo Board using the HT66F50. Operating Principles HT66F016L Features Operating Voltage f SYS = 4MHz : 2.0V~3.3V f SYS = 8MHz : 2.2V~3.3V f SYS = 12MHz : 2.7V~3.3V Three oscillators External crystal -- HXT Internal RC -- HIRC Internal 32kHz RC -- LIRC Fully integrated internal 8MHz oscillator requiring no external components Flash Program Memory : up to 2Kx16 RAM Data Memory : up to 128x8 EEPROM Memory : 64x8 Two external interrupt lines shared with I/O pins Multiple Timer Module for time measure, input capture, compare match output, PWM output or single pulse output functions HT66F50 Features Operating Voltage f SYS = 8MHz : 2.2V~5.5V f SYS = 12MHz : 2.7V~5.5V f SYS = 20MHz : 4.5V~5.5V Up to 0.2 s instruction cycle with 20MHz system clock at V DD = 5V Five oscillators External crystal - HXT External kHz crystal - LXT External RC - ERC Internal RC - HIRC Internal 32kHz RC - LIRC 1

2 Fully integrated internal 4MHz, 8MHz and 12MHz oscillators require no external components Flash Program Memory : 1Kx14 ~ 12Kx16 RAM Data Memory : 64x8 ~ 576x8 EEPROM Memory : 32x8 ~ 256x8 Multiple pin-shared external interrupts Multiple Timer Modules for time measurement, input capture, compare match output, PWM output or single pulse output functions Remote Encoding Description Presently available common infrared signal transmission protocols include those from ITT, NEC, Nokia NRC, Sharp, Philips RC-5, Philips RC-6, Philips RECS-80 and Sony SIRC etc. In order to transmit higher integrity signals, the remote control binary code is modulated onto a higher frequency signal and then sent out to the receiver using an infrared transmitter. Commonly there are two ways to modulate the signal, one is using Pulse Width Modulation or PWM, where the information is contained in the pulse width. The other is using Pulse Position Modulation or PPM where the information is contained in the time interval between the pulse trains. In this application, the HT66F016L MCU is used to encode using the NEC protocol using PPM modulation. The following content mainly illustrates the NEC protocol and PPM modulation function. Carrier Commonly carrier frequencies include 33kHz, 36kHz, 36.6kHz, 38kHz, 40kHz, 56kHz and no carrier, which have a common duty cycle of 1/2, 1/3. In this application example, the remote encoding transmitter Demo Board uses a 38kHz carrier frequency and a 1/2 duty cycle. NEC encoding format and PPM modulation description The protocol format start code + 16 bits user code (address code) + 8 bits command code(data code)+8 bits data code reverse code. The start code contains a carrier waveform of 9ms and a shutoff time of 4.5ms. 2

3 The address has a total of 16 bits, the lower 8 bits are followed by the higher 8 bits. There are 8 bits of data code and a corresponding 8 bits of reverse data code After transmitting the data reverse code, the stop signal high level has a duration of 0.56ms. PPM debug definition bit: bit 0 = high level with 0.56ms + low level with 0.565ms ; bit 1 = high level with 0.56ms + low level with 1.69ms The key output generally has two methodologies. One is where a complete data frame is output each time a key is pressed. The other is when, after a complete data frame is transmitted if the key is still pressed, a repeat code transmission will not stop until the key is released. If it is detected that the data is transmitted repeatedly, then the repeat data is transmitted once every 108ms, however the data transmission format will be as follows: The complete transmission waveform, including the repeat code, is as follows: 3

4 Remote decoding Description After the signal is received by the infrared receiver, the infrared remote transmission signal is transformed into a signal waveform, which will be input to the HT66F50 MCU on the PA3 pin, which is an external interrupt pin. The decoding program will convert this signal to actual data and determine whether the data is correct. If the data is correct, it will be displayed. If the data is incorrect, it will wait for further incoming signals. Note that, if the received waveform and the infrared transmission waveform are inverted and there is no carrier at a high level, the decoding diagram will be as follows: Address Code=0x00ff; Data Code=0x12 Hardware Circuit and Description Hardware Block Diagram and Description Encoding Block Diagram There are three parts in the encoding block diagram: A.Key matrix B.Peripheral boost circuit C.Infrared transmission 4

5 Decoding Block Diagram There are two parts in the decoding block diagram: A.Infrared signal receiving B.Data display Encoding and Decoding Circuit and Description Encoding Circuit 5

6 Remote Controller Transmission Description: The HT66F016L is a 0.9V Flash MCU. The entire system is supplied by a single cell battery with a voltage range of 0.9V~1.8V. A voltage generated by a DC to DC converter is supplied to the MCU and the peripheral devices (VOUT/VCC). The voltage value is controlled by software (DCVS2~DCVS0 bit in the DCC register) as follows: When a key is pressed for a long or short time, IR_OUT, which is the infrared remote transmission head, will send an NEC encoding signal to the receiving side and implement the corresponding operations. If no key is pressed for about 3s, the system will enter a power down condition (sleep0 mode). When any key is pressed, the system will be woken-up on the PA0~PA3 falling edges. 6

7 Decoding Circuit Remote Controller Receiver Description: (1) The HT66F50 is supplied by 5V. The 7-segment LED displays the received data using PB0~PB2, PC0~PC7 and PD0~PD3. (2) The IR is the infrared remote receiving head, which has a receiver center frequency about 38kHz. When an infrared carrier of 38kHz is received, the VOUT pin will output a low level and drive LED1. (3) Data will be received on the HT66F50 PA3 pin. 7

8 S/W Flowchart Encoding Program Example Flowchart Start clr RAM Initial I/O Initial TM1 The Key is pressed? (Key scan about 3s) Y Transmit remote signal N Enter halt(sleep0) Wait for pressing key wake-up The key is pressed for long time? N Y Transmit repeated code N The key is released? Y Transmission Procedure illustration: (1) Initialise all the I/O ports, RAM and TM registers. Execute the Key Scan program for about 3s. If a key is pressed during this period, transmit the data and determine whether it is pressed for long time. If so, then transmit a corresponding signal. If there is no pressed key, the system will enter the sleep 0 mode and will not be woken-up until a key is pressed. Wake-up Process: The program will execute a key scan operation for about 3s. If no key is pressed during this time, the system will enter a power down mode(configure PA0~PA3 to have a wake-up function and configure the PB port to be output low). When any key is pressed, the PA0~PA3 ports will experience a high to low edge and generate a falling edge wake-up. 8

9 Decoding Program Flowchart Main Program Flowchart TM0 Interrupt Service Subroutine Flowchart ISR_STM Count RTm0cnt++; _t0af=0; _mf0f=0; return 9

10 INT0 Interrupt Service Subroutine Flowchat Receiver Procedure: (1) Initialise all the I/O ports, RAM, TMR and INT registers. (2) The main program will always determine the receiver finish flags, Fir_ok and repeat transmission flag, Fir_repeat. If Fir_ok=1, the received data will be seen to have finished and it will then determine if the data is correct or not. If it is correct, then it will be displayed. If Fir_repeat=1, the data will have been transmitted repeatedly and the display remains unchanged while the DP display will flash. (3) Timer0 is used for timing. It always remains on and has one interrupt every 40 s. (4) The received code is received via the interrupt pin. In the interrupt service program, the RTm0cnt value is determined whether it is in the data receiving range. If it is, set the Fir_ok and Fir_repeat flags after the data is received. If it isn t, exit the receive process and wait for the next data reception. 10

11 Program Example 1. The Configuration Option for the decode program is shown below. ;================================================================ ;CONFIGURATION OPTION: ;SysVolt : 3.3V ;SysFreq : External XTAL ;WDT : By S/W Control(Disable) 2. The Configuration Option of the encoding program i s shown below. ;================================================================ ;CONFIGURATION OPTION: ;SysVolt : 5.0V ;SysFreq : HIRC 4MHz ;WDT : Enable ;I/O or Reset function: I/O ;LVR function:disable ;SIM function:disable ================================================================= Conclusions This application describes how to use the Flash MCUs (HT66F016L&HT66F50) to implement simple remote encoding and decoding with the text and the program example, for readers reference. Accessory Encode Program HT66F016L master.zip Decode Program HT66F50 slave.zip 11