The HT6P20x2 Encoder IC

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Blaise Lawrence
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1 The HT6P20x2 Encoder IC D/N:AN0261E Introduction Holtek s HT6P20x2, wireless remote control encoding IC, is capable of supporting up to a 22 bit address code and a five bit data input code. The device includes additional advantages such as a wide operating voltage range of 2V~12V, low power consumption, integrated RC oscillator, high noise immunity etc. The devices can be used in applications such as car alarms, motorcycle/electric bike alarms, home security and gating products, window remote control, doorbell remote control to name but a few. Operation Declaration IC Selection Table The HT6P20x2 series of devices are packaged part numbered according to their different Address Code Bits and Data Code Bits as shown in the following table: Part Number Address code bits Data code bits HT6P20B HT6P20D HT6P20F The corresponding pin assignments are illustrated as below: 1

2 Signal Trigger The data input lines, D0~D4, in the HT6P20x2 are all connected to a pull-high resistor. Under non operational conditions, the data inputs, D0~D4, will therefore remain at a high level. After the device receives any or multiple high to low switch triggers on the D0~D4 lines, the device will start then to execute its internal encoding function and output its corresponding address and data codes on the DOUT pin. As long as these D0~D4 lines remain at a low level, the address and data codes will be transmitted continuously. The timing of this protocol is shown in the figure below. From the above figure, the DOUT data output of the encoding device is connected with the trigger time of the data input pins as described below: When the trigger time of the data inputs, D0~D4, is shorter than one pilot code, the DOUT output pulse length will be the same as the data input trigger which means that it will be unable to transmit a complete pilot code. When the trigger time of the data inputs is longer than one pilot code and smaller or equal to one code length, then the DOUT output will output a complete data code. When the trigger time of the data inputs is longer than one complete code, the DOUT output time will be the same as the data inputs (D0~D4.) As long as the data inputs trigger continues, then DOUT will continue to output data. The diagram below shows three complete transmission signal code words: Note:If the data line remains at a low level, then the signals will be output continuously. One code word is a packet of information composed of a pilot code, an address code, a data code and an end code among which the pilot and end codes are the same in all of the HT6P20x2 series of devices. A complete code word breakdown is shown below: 2

3 Pilot Code Each transmission has a pilot code preceding the address and data codes. This is to alert the decoder that address and data codes are about to be transmitted. The pilot code waveform is composed of a low pulse of 23λ duration followed by a high pulse of 1λ duration. A 1λ time unit is equal to 32 internal oscillator time periods. When the data (D0~D4) input pins change from high to low, note that the duration of the data input must be greater than the pilot code length for a full signal transmission to occur. If the input low signal is less than the pilot code length by 768 clock oscillator periods, then DOUT will only output a pulse smaller than the pilot code and no address, data or end codes will be transmitted. Address/Data Bit Waveform As address/data bits can be designated to be either 0 or 1 which must be encoded in a certain way. One bit of data consists of one pulse cycle (which includes a certain ratio of one low pulse and a high pulse) with each pulse cycle having a duration of 96 internal oscillator periods. This means that one bit of data, either 0 or 1, must be completed in 96 oscillator periods. The following figure depicts the 0 or 1 waveforms showing the high/low level ratio. Note: 1λ = 32 internal oscillator time periods. Bit 0 consists of a low pulse for 1λ then a high pulse for 2λ, marked as t DW in the figure. Bit 1 consists of a low pulse for 2λ then a high pulse for 1λ, marked as t DW in the figure. 3

4 End Code Waveform After the data/address codes from the HT6P20x2 series of devices are transmitted, a 4 bit end code with the bit pattern 0101 will be transmitted to complete the full code word transmission as shown below. Operation Flowchart The flowchart describes the HT6P20x2 operation flow. After power on the device enter the Stand-By Mode. A transition on the signal input pins, D0~D4, from high to low will wake up the device at which point it will enter its transmission encoding mode and transmit a full code word consisting of a pilot code, address code, data code and end code. After a code word is transmitted, check if the signal input pins, D0~D4, are still receiving input signals. If yes, then keep transmitting code words or else return to the Stand-By mode. Power ON Stand-by Mode No Data Input Pin in Low State Yes 1 Word of Pilot code/address/data/end Code Transmitted No Data Input Pin Still in Low State Yes 4

5 Typical Circuit HT6P20B2 For a battery voltage between 2V~12V, a recommended application circuit is shown below for a frequency of 315MHz. Note: The RF circuit component values are for reference only. Users should modify the values according to different frequency and voltage applications. HT6P20D2 For a battery voltage between 2V~12V, a recommended application circuit is shown below for a frequency of 315MHz. 2.2uH ANT 10p 2.5p 1.5p 2SC3356 5p 10n 56K 220 HT6P20D2 1 8 VDD NC 2 7 VSS D3 3 6 DOUT D2 4 5 D0 D1 S4 S3 S2 S1 VBAT 100 LED Note: The RF circuit component values are for reference only. Users should modify the values according to different frequency and voltage applications. 5

6 HT6P20F2 For a battery voltage between 2V~12V, a recommended application circuit is shown below for a frequency of 315MHz. Note: The RF circuit component values are for reference only. Users should modify the values according to different frequency and voltage applications. Application Example From the above information, this application will construct a remote controller using the HT6P20x2. The data generated using the HT6P20x2 will then be received using a superregeneration RF receiver and decoded using an MCU which is the HT46R065 in this example. The decoded address and data will then be displayed on an 8 digit 7 segment display. Application Block Diagram Example Hardware Block Diagram 6

7 Hardware Description Transmission Code: When an input data change is detected on the HT6P20x2, the data and address codes will be transmitted using the RF resonator circuit. Receive Code: The HT46R065 MCU, in this example, receives the transmitted code from the HT6P20x2 through the superregeneration RF receiver module and displays it on the display after decoding. The decoding method uses a level time checking, interrupt timer and algorithm etc. This example uses an interrupt timer decoding method by reading the data level period using interrupts and then comparing the width of both high and low pulses in each bit (every pulse cycle) to implement data decoding. When using level period checking for decoding, note that as the internal clock in the HT6P20x2 is an internal RC type, then different voltages will affect the data level period. RF Transmit and Receive Circuit With the above information and using the accompanying typical circuit diagram, a common application program and common PCB can be designed that is compatible for the encoding devices such as the HT6P20B2, HT6P20D2, and HT6P20F2. The RF receiver in the application program uses a superregeneration receiver module with an MCU to decode the data and uses two seven segment displays to display the received address and data bits. After power on, select the decoding device, whether it be HT6P20B2, HT6P20D2 or HT6P20F2, using the through input pins. The selected device will be displayed on the display. After the RF signal is received, the buzzer will beep once, and the original displayed device number on the display will disappear and be replaced by the address code decoded from the RF signal in addition to the corresponding input switch value. To display the HT6P20B2 22 bits of address code requires six digits. The 7 th digit will display a 6 to indicate that there are six digits to display the address, while the 8 th digit shows the switch value of 1 or 2. The 20 bit address code of the HT6P20D2, requires a 5 digit display and will and show 5 on the 7 th digit to indicate that there are five address digits to be displayed. The 8 th digit shows the switch value of 1 ~ 4. The 19 bit address code of the HT6P20F2, requires a 5 digit display and will show 5 on the 7 th digit to indicate that there are five address digits to be displayed. The 8 th display shows the switch value of 1 ~ 5. 7

8 Application Flowchart The flowchart for the application program is composed of two parts, the main flowchart and the interrupt decoding flowchart. Main Flowchart After the main program initializes the MCU and related control flag bits, read the data/address codes by checking the PGM_OK flag bit. Only after two successive readings of the same data/address codes will the decoding be considered to be successful after which the decoded data/address codes will be shown on the display. After the decoding is complete, the program will keep checking if the data is the same as the previous decoded data. If it is the same, then the program will remain in the checking loop. Only when a difference between present data and the previous is detected will the program initialize the related control flag bit. After the data is decoded it will be displayed. 8

9 9 The HT6P20x2 Encoder IC

10 Interrupt Decoding Program Flowchart The example uses Timer1 to setup a time of 50us to check for transitions on the I/O pin for decoding. When a transition on the I/O pin level is detected, then check the times of the two levels. After checking the length and comparing twice, determine if the bit is either a 1 or 0. After all the encoded data sent from the HT6P20x2 has been decoded, set the PGM_OK flag bit to indicate the completion of an address/data transmission. During decoding, if an external interrupt code or pilot code occurs, then as this time will exceed the level maximum duration, the program will initialise the decoding related registers and flag bits and not restart decoding until it is complete. Check the following program example description for details. Program Description The program here is composed of a main program and an interrupt decoding programs. In the main program, the flag bits will be initialized and the TMR enabled and check for reception of data from the HT6P20x2. Check for one decoded data reception using the PGM_OK flag and then disable the TMR. After reading the data, setup the related flags, enable the TMR, then read the data again and disable the TMR. If the data is the same, then show the decoded data/address codes on the eight digit display, or enable the TMR to recheck the codes. For details see the attached program file and the TMR decoding flowchart. 10

11 Interrupt decoding program: Use the TMR function of the MCU to receive the RF signals from the Encoder at every Time Out and decode the encoded signals using the following program and convert it to a format for suitable display or for control signals. ;TMR Interrupt subroutine: ;0C TIMER1 INTERRUPT(Time control) TIMER1: CLR WDT PUSH ;Judge the signal input : MOV a, 56 MOV TMR0,a SNZ SIO_PIN ;Scan the SIO pin status JMP SIOPIN_LO ;If the SIO pin is low jump to SIOPIN_LO level ;Count remained at high level to receive the signal duration: SIOPIN_HI: SNZ SIO_STATUS ;Check the SIO pin former status JMP SIOPIN_LO2HI SIOPIN_HI2H: INC HI_COUNT SZ Z DEC HI_COUNT ; Max. count is FFH JMP EXITINT SIOPIN_LO2H: SET SIO_STATUS ;Change to the current status XMOV HI_COUNT_SAVE,HI_COUNT ;Save LO_COUNT CLR HI_COUNT ;Refresh LO _COUNT LSERJ HI_COUNT_SAVE,MAXDURATION ;If LO_COUNT_SAVE is smaller than the MAXDURATION JMP SIO_COUNT_INITIAL ; Code is wrong ;Compare the ratio of the high and low signal levels and thus determine if it is "1" or "0" LBERJ LO_COUNT_SAVE,HI_COUNT_SAVE ;If LO_COUNT_SAVE>HI_COUNT_SAVE,Write "0" TO C JMP SIO_0_CODE ;else write "1" TO C JMP SIO_1_CODE ;Count remained at low level to receive the signal duration: SIOPIN_LO: SZ SIO_STATUS ;Check the SIO pin former status JMP SIOPIN_HI2LO SIOPIN_LO2LO: INC LO_COUNT SZ Z DE LO_COUNT ; Max. count is FFH JMP EXITINT ;Exit TMR Interrupt SIOPIN_HI2LO: CLR SIO_STATUS ;Change to the current status XMOV LO_COUNT_SAVE,LO_COUNT ;Save HI_COUNT 11

CLR LO_COUNT ;Refresh HI_COUNT LSERJ LO_COUNT_SAVE,MAXDURATION ;If HI_ COUNT _ SAVE is smaller than the MAXDURATION JMP SIO_COUNT_INITIAL ; Code is wrong JMP EXITIN ;Exit TMR Interrupt SIO_0_CODE:

12 CLR LO_COUNT ;Refresh HI_COUNT LSERJ LO_COUNT_SAVE,MAXDURATION ;If HI_ COUNT _ SAVE is smaller than the MAXDURATION JMP SIO_COUNT_INITIAL ; Code is wrong JMP EXITIN ;Exit TMR Interrupt SIO_0_CODE: CLR C JMP $+2 SIO_1_CODE: SET C RLC ENCODER_DATA[3] ;Store data code RLC ENCODER_DATA[2] ;Store address code RLC ENCODER_DATA[1] ;Store address code RLC ENCODER_DATA[0] ;Store address code SDZ BITCOUNTER ;Code length counter JMP EXITINT ;Exit TMR Interrupt SET PGM_OK ;PGM_OK flag is set high JMP EXITINT ;Exit TMR Interrupt ;Input signal does not meet the proportional requirements for an encoded bit code, or to realize pilot code will jump to the loop to execute SIO_COUNT_INITIAL: XMOV BITCOUNTER,CODELENGTH ;Code length set CLR ENCODER_DATA[0] ;Clear register CLR ENCODER_DATA[1] ;Clear register CLR ENCODER_DATA[2] ;Clear register CLR ENCODER_DATA[3] ;Clear register CLR PGM_OK JMP EXITINT ;Exit TMR Interrupt ;Leave TMR interrupt EXITINT: POP RETI ;========================================== PCB Layout Notes The figure below shows an example of the Encoder (HT6P20x2) Transmitter Layout. The frequency is 315MHz. See the attached file for more information. 12

Component Placement The first consideration for component placement are their signal lines which must be as short as possible The routing space for the VCC and GND lines should be reserved in advance

13 Component Placement The first consideration for component placement are their signal lines which must be as short as possible The routing space for the VCC and GND lines should be reserved in advance In addition to the antenna matching components, the RF PAOUT pin area should avoid being occupied with components which may influence proper RF operation. Routing As right angles more easily accumulate charge, they will have larger discharges which will influence PCB stability. It is recommended to conduct all routing using 45 degree bevels or curves. The distance between tracks should not be less than 6 mils The distance between the wires and the apertures should not be less than 6 mils The distance between two linked apertures should not be less than 6 mils The width of the VCC and GND tracks should not be less than 12 mils Each IC power source must have a decoupling capacitor located adjacent to the IC The RF antenna trace should not have a ground plane so as not to affect performance Antenna Stock dipole 50 SMA plug for the Patch Antenna λ/4 width of copper wire, single core wire, stranded wire RF antenna PCB layout Antenna width = 35mil (min) Antenna length (L) formula is ((Lightspeed)/(4*f* )),ε= 4.7 for FR4 material of PCB; f = resonance frequency. ANT Layout Example Conclusions The above example has introduced the HT6P20x2 related features and encoding principles as well as an encoding and decoding example description for the user to refer to when implementing actual application development. 13

Using the 315M/433MHz ASK Transmitter HT4xR01T3 MCU

Using the 315M/433MHz ASK Transmitter HT4xR01T3 MCU D/N:AN0205E Introduction Holtek s HT46R01T3 and HT48R01T3 are OTP (One-Time Programmable) type versatile MCUs, whose internal ASK RF transmitter includes