System Design Based on SAA7214 and SAA7215 Set Top Box

Abstract: This article introduces the features and structure of the SAA7214 and SAA7215 chips from PHILIPS for interactive digital TV applications. The scheme of interactive digital cable TV set-top box composed of the two is proposed, and the specific software and hardware system components are given.
Keywords: cable TV; set-top box; system; audio; video

0 preface

With the continuous development of information technology, communication technology, television technology and computer technology have entered a new era of mutual integration. Interactive TV (ITV) is the embodiment of this combination. The so-called interactive TV is a kind of TV controlled by the user. The user can make choices and decisions between programs and programs. It is a new type of television technology with asymmetric duplex communication mode. Among them, digital set-top box (STB) is one of the key technologies to realize interactive functions. As a user terminal in an ITV system, it is a bridge between ordinary TV and broadband transmission networks. By sitting in front of the TV in the home, STB users can realize a variety of services such as video on demand (VOD), home shopping, home office, electronic games, etc., and can also see high-definition digital TV programs on ordinary TV sets.

1 SAA7214 and SAA7215 features and structure

The SAA7214 and SAA7215 are a set of STB solutions from PHILIPS. The former is responsible for real-time requirements for higher hardware demultiplexing, video and audio source decoding, and separation of video and audio data streams, as well as peripheral I/O device control associated with decoding. The latter is responsible for the decoding, encoding of audio, video and graphics, and splits the decoded data stream into audio and video signal outputs.

1.1 SAA7214 Features and Interfaces

The SAA7214 is mainly used to transmit the source decoder of MPEG-2 format information. The SAA7214 includes a MIPS PR3001 chip, a RISC-size CPU with a built-in control of 32-bit, millions of instructions per second. The chip operates at 40.5 MHz. The SAA7214 also includes Universal Asynchronous Receiver Transmitter (UART), I 2 C unit, and IEEE1284 interface. The serial communication controller of the SAA7214 includes three UARTs. It has two UART-characterized TxD and RxD pins and supports automatic data flow control via two data lines, RTS and CTS. The other UART is the only duplex interface (TXD, RXD) and supports RTS, CTS data flow control. The UART can also work in two-wire mode, and in this way they simply receive and transmit data via RXD and TXD. The SAA7214's I 2 C controller includes two serial interfaces, which are suitable for I 2 C bus specifications and support standard and fast I 2 C bus modes. In the same bus case, operation can be performed in either the main transmitter mode, the main acceptor mode, the slave transmitter mode, or the acceptor mode by different programmed I 2 C logic.

1.2 Functional characteristics and structure of SAA7215

The SAA7215 is a source decoder for MPEG-2 format including audio decoding and video decoding. In addition to some basic MPEG features, the SAA7215 provides enhanced graphics, background display, and full-screen display methods like encoded output video. Thanks to the best structure for audio and video decoding, it is possible to support chart processing in terms of external memory and CPU processing power.

The SAA7215 has a complete memory structure for 16Mbits for low-end devices and 32Mbits for mid- to high-end devices, so it can handle and control MPEG data streams and charts. It also provides the CPU with high bandwidth and short latency when accessing the chart registers. The SAA7215 integrates a video encoder with Y/C, CVBS and RGB outputs. The SAA7215 has the following features:

(1) There are single or two external synchronous DRAMs. Since the memory is effectively used in the MPEG decoder, there is more than 1 Mbit of storage space for chart processing, and the available storage space in the dual SDRAM configuration is 17 Mbit.

(2) In PES or ES in byte-wide or serial-bit format, there are input devices dedicated to compressing audio and video, and strobe signals are used to distinguish between video and audio data.

(3) Flexible memory allocation can best distinguish the memory of different tasks.

(4) Support boundary scan test and external SDRAM self test.

2 System hardware design based on SAA7214 and SAA7215

According to the functional characteristics of SAA7214 and SAA7215, the hardware circuit of the system adopts modular structure design, which is mainly composed of four parts: communication module, main control module, control panel module and IC card module. Each module can be replaced independently.

2.1 communication module

The communication module specifically includes: a QAM demodulator and a telephone board (or a bidirectional module).

The QAM demodulator can output the QAM modulated signal transmitted by the HFC network after tuning frequency conversion, QAM decoding, deinterleaving, RS decoding, descrambling, etc., and output the standard code stream before MPEG-2 demultiplexing. (ie TS stream). This part is mainly done by a piece of VES1820X chip.

The telephone board adopts DTMF mode to modulate the uplink signal, and uses the telephone network as the uplink channel and the downlink to adopt the digital modulation mode of 64QAM. After the two-way transformation of the cable television network, the two-way module can be used to implement the interactive function, and the two-way module uses the BPSK method to modulate the uplink signal, and the cable television network is used as the uplink channel.

2.2 main control module

Main control module: specifically refers to the main board. It mainly consists of SAA7214, SAA7215, UDA1320A chip and memory.

The SAA7214 chip can decode the TS stream from the MPEG-2 source and separate the video and audio data streams, as well as the control of the peripheral I/O devices associated with the decoding.

The SAA7215 is responsible for the decoding and encoding of audio, video and graphics, and divides the decoded data stream into audio and video signals, which are output by the SAA7215. The SAA7215 also has a complete memory structure, using DRAM, SDRAM, FLASH, etc., through these memory chips, the software runs faster.

The audio signal is output by the UDA1320A. UDA1320A is a single-chip positive-phase stereo DAC with bit stream conversion technology. It has low power consumption and low voltage operation mode; system clock with three different frequencies of 256, 384 and 512; different can be selected by static pin control Frequency; supports sampling frequency from 16KHZ to 48KHZ; integrated digital filtering and normal phase DAC.

2.3 control panel module

The control panel module includes: a keypad and a display panel. It controls the functions of the panel through an AT89C2051 microcontroller and is associated with the SAA7214 in the motherboard module. The demodulated, decoded and encoded video and audio signals (ie, analog signals) are respectively outputted from respective ports of the set top box to complete function control and display of the STB. At the same time, the remote control can be used to control and switch all basic functions.

2.4 IC card module

IC card module: refers to the IC card board, with intelligent IC card CA descrambling function. The board uses the TDA8004 interface chip, which is located between the IC card and the microprocessor, and can be protected and controlled without a large number of external components. The signal is connected to the SAA7214 in the mainboard through the interface, and has a corresponding permission confirmation function. When the set-top box receives the permission confirmation information, the digital television program is decoded for the user to watch. Conditional reception and decryption processing is realized, so that services such as pay television, pay-per-view, and subscription can be realized through the IC card.

3 system software structure

The software structure of the set-top box system can be divided into three levels: business software application layer, real-time event processing layer, system kernel and driver layer.

Business software application

Real-time event processing layer

System kernel and driver layer

Hardware layer

3.1 business software application layer

The business software application layer is a layer of interface that covers the driver and the operating system. It is developed according to the system business needs, and implements various functions of the set-top box for the user application. Such as comprehensive information, e-commerce, video games, etc.
   
3.2 real-time event processing layer

The real-time event processing layer is a software environment that isolates the application from the low-level operating system and hardware details. It makes the application independent of the specific hardware platform and is the middleware of the business software application and the hardware platform. OpenTV middleware is used. OpenTV middleware provides the user with a complete application interface for the application, allowing the application to implement all the functions of the set-top box system simply by calling these functions. This makes the work of the user application part very simple.

3.3 system kernel and driver layer

The operating system used in this system is pSOS, and the hardware driver layer is mainly for various hardware modules and provides corresponding drivers. The main drivers include: interface modules, including I 2 C interface operation control, smart card control, etc.; audio module; video module; demultiplexing module; decoding module, Flash driver module.

4 Conclusion

The system structure and function block diagram of cable TV set-top box software and hardware based on SAA7214 and SAA7215 chips are introduced above. The system adopts a highly open modular structure design. The front end of the system compresses the analog video and audio signals into digital signals through MPEG-2 video coding, and multiplexes the multiple digital signals through the multiplexer before performing QAM modulation transmission. As the user's downlink digital signal. The user uses the telephone DTMF or BPSK as the uplink, and the user's selection information can be transmitted to the system service center (system front end) through the uplink channel. In this way, interactive video on demand (VOD), stock information and analysis and timely transactions, distance education, and information transmission can be realized in a broadband network (both cable television networks). The operating system and application software of the cable set-top box can be broadcasted by the control server through the downlink channel. To expand the application capability of the set-top box, it is only necessary to modify or add the corresponding software, without major changes to the hardware of the set-top box. System upgrades bring convenience.

At present, the domestic broadcast television system has begun to change to digital TV. Although the digital application in the near future is more digital, the color TV is digitalized, but with the increase of user demand for functions and the richness of cable operators' services, Functional interactive cable set-top boxes are also becoming more widely used and have a larger market.

Information: Microcomputer Information



references:

[1]. SAA7214 datasheet http://
[2]. SAA7215 datasheet http://
[3]. RISC datasheet http://
[4]. VES1820X datasheet http://
[5]. UDA1320A datasheet http://
[6]. AT89C2051 datasheet http://
[7]. TDA8004 datasheet http://


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