CD2518 color TV controlled by I2C bus

Abstract: I2C bus control is a series of binary coded pulse signals, which are programmed to implement microprocessor-to-unit functions.Integrated circuitControl and information exchange to improve control system efficiency by replacing hardware with software. In order to control the TV signal, CPU is used.storageFor memory, through TV signal processing, color decoding, image playback, video playback, audio accompanying, remote control are completed, which simplifies the circuit, increases the function and improves the reliability of the product.

Keywords: I2C bus, pulse, E2PROM

Use I2C bus to design application, simplify hardware design, make user "foolish", in production, can save half adjustablepotentiometerIt greatly simplifies the adjustment process, has good product consistency, improves the reliability of the product, and has the function of fault self-check, which can shorten the repair time and improve the repair rate.

I. I2C control system for CD2518 color TV

The control system of I2C bus of color TV is composed of hardware circuit and software data system. The hardware circuit is composed of master microprocessing integrated circuit, memory integrated circuit, controlled unit functional integrated circuit, signal transmission circuit and so on.Power SupplyPower supply circuit composition; Software data systems are composed of a number of groups of binary codes with specific meanings. CD2518 color TV is mainly composed of CPU LC863328, memory AT24C08, TV signal processor LA76810, sound control CD4052, etc.Integration BlockThe control system consists of CPU, memory and I2C bus control to complete color decoding, image playback, video playback, sound accompanying and remote control. Line and field scan, digital filter delay network is applied to integrate all small signal processing into a single chip, so that the circuit volume is reduced and the function is complete. A digital automatic synchronization circuit is used to obtain a stable field frequency signal, which ensures the stability of interlace scanning and improves the degree of automation. Functions such as playback, video detection and AFT are accomplished with integrated circuits, which simplifies the circuit and brings greater convenience for use and debugging. Memory AT24C08 assists CPU to complete automatic remote control system, which enables 255 channels to store multi-production tests (PAL, SECAM, B/G, D/K, NTSC, etc.) with multilingual functional representation and pull-downswitchFunctions such as machine, game and calendar allow full automatic search, semi-automatic search, fine-tuning/manual search. Its I2C bus control diagram is as follows:

2. Working principle of CD2518 color TV

(1) Working principle of LC863328

It is a full-system decoding integrated circuit, which is composed ofControllerAnd the calculator. Controller is a component that consents to command and control the operation of a microprocessor, receives step-by-step instructions from memory, decodes instructions, and sends out all the internal control information required for various operations and the control signals required for the external CPU at a specified time through a timing and control circuit to coordinate the various parts and complete the various operations specified in the instructions. Operators are operations/logical parts ALU, accumulator ACC, and temporary memory that are used to perform arithmetic and logical operations. It has interrupt function, real-time control of multiple controllers to take instructions, analyze instructions and execute instructions for programs written by people, read control data from memory, send to controlled circuit, adjust various indicators through I2C bus application software, and restore the image to state.

The I2C bus interface circuit of CPU is mainly composed of address register, move to bit register, serial data register, serial port control register, input/output channel selector, andWave filterForm. Shift registers are connected with data registers in parallel and SDA in serial mode. They are used to output parallel serial data in parallel. The capacity of shift registers is 9 bits. It can store an 8 bit data byte to be sent and a 1 bit promised ACK signal. The shift registers are generated and identified by the I2C bus control circuit. Shift data from right to left to reach SDA and allocate it to SDA0 and SDA1 by the channel selection control circuit. The serial port data register stores an 8 bit from the CPU and a data byte just received waiting for the CPU degree curve. Data registers are used to judge the running state of I2C bus interfaces and call corresponding operation handlers based on these dataModularTo complete the data transfer operation of the interface; The control register provides functions such as I2C bus input and output channel selection, response bit selection, serial port clock cycle selection, etc. Address register loads 7-bit address; The input filter has an I2C bus logically compatible input level.

All controlled integrated circuits on color TV CD2518 are connected to LC863328 on two buses. Control information is transmitted by software pulse data. 29-foot serial data line SDA and 30-foot serial clock line SLC are pulled up by one pull-up respectively.resistanceThe RP is connected to the front end of the power supply. When the bus is idle, SDA and SCL must remain at a high level.

The 27-foot data cable and 28-foot clock clock line in LC863328 read the line instructions from the memory according to the values in the program counter PC, send them to the instruction register, and then decode the instruction opcode after taking it out, analyze its instruction properties, and after taking out the operands, operate on the operands according to the nature of the operation code and execute the instructions. 22, 23, 24, 25 feet control the output of the character tricolor signal with programmable polarity; Receive input of remote control signal through 34 feet to adjust the whole set signal parameters. Place input under 14 foot control and adjust progressively during on-site sweep to lock the line PLL; 15 feet control AGC to ensure the output video amplitude is unchanged; The field and line signals are input from 20 or 21 feet to get synchronous pulse, which makes the output of stable line and field deflection signals under different video input conditions. With 40, 41, 42 feetHigh frequency headBand control.

(2) The structure and working principle of AT24C08.

AT24C08 is an erasable, writable, read-only memory that transforms read and write functions directly by changing device address codes in SDA on the I2C bus. When the serial clock line SLC inputs a positive edge clock signal from six feet, the data enters each E2PROM period, and when the negative edge clock, the data is output from each device. The 5 legs are driven by open drain circuit and 1, 2 and 3 legs are used as device address input when SDA is transmitted in both directions by serial data line.

The structure of AT24C08 is mainly composed of the E2PROM storage array, its X-direction and Y-direction decoding circuit, power pump/timer, serial multi-channel modulator, data register and I2C bus control logic for start, end, address comparison, serial control, data loading register and output, responseLogical circuitForm. The setting of the power pump exempts the writing of high voltage power supply set up; Data registers guarantee the loading space for page-written data. Device Address Comparator is used to identify your own slave address.

The working principle is divided into four parts:

(1) Select from address

AT24C08 is an I2C interface device with address 1010 assigned according to the address of Philips I2C interface device. In addition to addressing bytes (after SLAR/W), the memory attached to the I2 bus uses an address of WORDADR bytes for the in-chip address, so the in-chip address range is 256 bytes. AT24C08 has a storage space of 1K bytes.

(2) Page writing function

When E2PROM writes, it always takes a certain amount of writing time (5-15ms), so it is not possible to write more than one data byte continuously in the writer. A data register with a certain capacity is installed in the E2PROM device. When a user writes E2PROM data bytes no larger than the number of page-write sections, they can load into the data register in E2PROM at the writing speed of normal RAM, and then start the automatic write timing control logic, which automatically writes the data in the data register to the specified unit in E2PROM after 5-10ms. AT24C08 has 16 page-writing sections.

(3) Flip-up of page address space

Data registers have 2, 3, and 4-bit page addresses, respectively, corresponding to the number of page-write sections. Is the position part of the word address. When writing, the written data is defined as the low part of the page address space and data register address of the data register according to the word address (WORDADR). When overflowing, it will not carry into the high part of the word address, which results in a "rollover" of the written data in the address.

(4) Data operation format

1. Writing Period Time Series of E2PROM

Due to the setup of page write function, the I2C bus only loads its data registers for AT24C08 operation. After the data is loaded and E2PROM receives the stop bits sent by the I2C bus, it automatically starts an internal synchronous write cycle, writes data from the data register into the E2PROM array, and all inputs in this internal write cycle are invalid. AT24C08 does not allow bus responses until the end of the write cycle. Write cycle time series as shown in Figure 2

(3) Working principle of LA76810

Under the control of I2C bus, LA76810 completes the processing of image, audio IF signal, video and scan signal. After the TV IF signal is input by 5 or 6 feet of LA76810, it is processed by internal image IF AGCamplifierAmplify, the PLL phase-locked loop demodulates the video signal and the second audio intermediate frequency signal. After the second audio intermediate frequency signal is demodulated, amplified and controlled by the PLL circuit, the audio signal is output from one foot of LA76810 to the audio power amplifier circuit. Video signal is output from 46 feet and then returned from 44 feet. After PAL, NTSC decoding, picture quality improvement processing circuit and R, G, B matrix decoding circuit output R, G, B basic color video signal from 19, 20, 21 feet, feed into the video amplifier and amplify in colorPicture tubeThe cathode generates an excitation signal to complete the function of color image transmission. Line and field scan small signal generation of LA76810 is accomplished by frequency division lock of 4MHZ clock signal, without external line oscillationcrystal; After the video signal is processed by the synchronization separation circuit, the line and field synchronization signals are obtained respectively to realize the line and field scanning synchronization function. The generated line and field excitation pulse signals scan the excitation signal from 23 foot output field, and 27 foot output line scan excitation signal.

(4) Working principle of CD4052

CD4052 Multiplex Logic Digital Circuit Integrated Switch, used to select and mix analog and digital signals, controlterminalAfter the digital signal is transformed by logical level, the function of small logical amplitude switching and large signal amplitude switching can be achieved. The logical control end of CD4052 is 6, 9 and 10 feet. When 6 feet are low level, 13 and 3 feet of the common terminal are connected with other feet by controlling the potential changes of 9 and 10 feet to achieve the purpose of signal selection. When 6 feet are high level, no matter how the potential changes of 9 and 10 feet, 13 and 3 feet are not connected with other feet.

3. Functions of CD2518 color TV

1. Language function, the characters displayed on the screen can be switched between Chinese and English.
2. Calendar function, when Chinese OSD is displayed, lunar calendar will appear, while when English OSD is displayed, lunar calendar will not appear.
3. Game functions.
4. Fortunately select a number operation, select "Number range" or the number of numbers after entering the number selection menu, use the volume function key to change the setting value, and the number is randomly selected by the MCU.
5. Select a strong reception function.
6. Automatic color recognition. Select different systems, sound accompanying and other functions as needed.
7. Select functions such as child lock, ZOOM, menu background, etc.
8. Stereo, bass or headphone selection function.

IV. Concluding remarks

By using I2C bus control system to design color TV, you can makeCircuit boardThe area decreases, the control function increases, and the failure rate is low. Software replaces hardware, eliminates the potential device aging, poor contact failure, and improves the overall stability; The design of the function module makes it very convenient to add or reduce the function circuit of the unit, which makes the product upgrade and replacement fast. Multi-master control enables automation of production, maintenance and debugging, and improves production efficiency. The bidirectional transmission of data eliminates the phenomenon of circuit out of control and improves the ability of fault diagnosis.