Principle and Application of OSD Chip MB90092

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Abstract: MB90092 is an OSD (On Screen Display) programmable LSI chip manufactured by FUJITSU Co., Ltd. in Japan. The function, pinout and working timing of MB90092 are introduced. MB90092 and AT89S52 are given. Interface circuit and programming design method.

Keywords: MB90092; OSD; video character overlay; AT89S52

In recent years, various digital video surveillance systems have been widely used in highways, power, banking and other fields. Digital video surveillance systems often use On Screen Display (OSD) technology to achieve human-machine interface interaction. In fact, the on-screen display technology superimposes text on the video image, so that the display screen can provide more additional information to the user.

MB90092 is a dedicated video character superimposing chip made by CMOS technology introduced by FUJITSU Corporation of Japan. The MB90092 integrates a display memory (VRAM), an external font interface, and a video signal generator. Externally, only a small number of components can be connected to display Chinese characters and graphics. It is powerful, easy to interface, easy to program, and easy to embed in a variety of digital video surveillance systems, so it can be widely used in various industries and various fields.

1 pin arrangement and internal structure

The MB90092 is available in an 80-pin QFP package. The pinouts are shown in Figure 1. The function of each pin is as follows:

1 pin (IC): internal color generation mode setting terminal;

2 feet (VOC): character interval signal output;

3 feet (VOB): character / background signal output;

5, 6, 7 feet (B, R, G): color signal output;

8 pin (CS): chip select signal, active low;

9-pin (SCLK): clock input, which reads in data on the rising edge of the clock pulse;

10 pin (SIN): serial data input;

12 feet (EXHSYN): external horizontal sync signal input port of the device;

Pin 13 (EXVSYN): external vertical sync signal input port of the device;

14 (HSYNC): horizontal sync signal output;

15 feet (VSYNC): vertical sync signal output;

16-pin (VBLNK): vertical space signal output;

17, 18 feet (EXS, XS): These two pins can be used for an external quartz crystal oscillator, and the NTSC system is connected to 14.31818MHz? PAL when connected to 17.734475MHz;

20 feet (FSCO): internal color pulse output;

21 pin (CBCK): external color pulse input;

22 feet (PDS): color pulse comparison output;

31 feet (YOUT): brightness signal output terminal;

32 feet (YIN): superimposed display brightness signal input;

34 feet (COUT): saturation signal output;

35 feet (CIN): superimposed display saturation signal input;

37 feet (VOUT): composite video signal output;

38 feet (VKIN): background level control input;

39 feet (VKOUT): background level control output;

40 feet (VIN): composite video signal input that needs to be superimposed;

43 feet (READ): read the external font control terminal, active low;

44~51 feet (DA0~DA7): external font data input terminal;

53~61 (63~64, 66~75 feet, ADR0~ADR20): external font address output;

77-pin (TSC): The external font operates on the bus control terminal. When this pin is low, the ADR0~ADR20 and READ pins are in a high-impedance state.

78 feet (TEST): test signal input;

79, 80 feet (EXD, XD): connected to an external LC oscillator circuit;

19, 25 ~ 28 feet (NC): empty feet;

11,42,62,76 feet (Vcc): power input (+5V);

4, 23, 52, 65 feet (Vss): ground terminal;

41 feet (AVcc1): composite video signal analog power supply;

33 feet (AVcc2): brightness and chrominance signal analog power;

24, 29, 30, 36 feet (AVss): analog ground.

The internal structure of MB90092 is shown in Figure 2. It mainly consists of serial input control circuit, NTSC/PAL signal generator circuit, display memory control circuit, display memory VRAM, font read operation control circuit, output control circuit, and video signal synthesizer. And analog switch components.

2 main features

The main features of MB90092 are as follows:

● Dual screen display function is available, and the main screen and sub screen can be displayed separately or overlappingly;

● Main screen display capacity: 24 characters × 12 lines (up to 288 characters);

● Character size has standard (24 × 32 dot matrix), double width, double height, double width × double height, four times width × double height and other modes;

● Character color: 8 different colors and 8 background colors can be set separately for each character;

●The display position can be arbitrarily set to the horizontal direction and the vertical direction, and the line spacing can be set at the same time;

● Both composite video signal and Y/C separated video signal input, composite video signal, Y/C separated video signal and RGB digital video signal output;

●The internal video signal generator can support NTSC or PAL system, and can choose progressive or interlaced scanning mode;

● It can communicate with external control system through three pins: CS, SCLK and SIN.

● The external command and data can be received by the serial input control module and decoded by the decoder and sent to each register;

● NTSC / PAL signal generator can generate NTSC / PAL system clock signal;

The display memory control module can generate a control clock signal for each module;

● The display memory VRAM can be used to store character codes, character colors, character background colors, features, and line control information;

The font memory control module can read the font data in the external font memory by using the address and the READ signal;

● The character data retrieved from the CGROM can be processed by the output control module, and the boundary of the character, the background, and the like are generated at the same time;

The video signal synthesizer generates a video signal and a luminance signal under the control of the internal synchronization signal;

The analog switch can be used to select whether to combine an external video signal or an internal video signal with a character signal.

3 MB90092 working sequence

The MB90092 video character superimposing chip receives external control commands and display data through three pins: CS chip select), SCLK (serial clock), and SIN (serial data). Each instruction of MB90092 consists of two bytes, the upper 5 bits of the first byte are the command code, and the remaining bits and the second byte are the data. Figure 3 shows the timing diagram of the external interface of the MB90092.

When the CS pin is low, the MB90092 reads data from the lowest bit of the SIN pin one bit at a time on the rising edge of each clock. After reading one byte, the CS and SCLK pins are asserted high, then the CS pin goes low and begins reading the next byte. In order to maintain byte synchronization, the CS pin should be asserted high and then asserted low before starting to transfer serial data. In addition, the SCLK pin should be forced high before serial data transfer, except when power is first applied.

The microcontroller sends instructions to the MB90092 through the serial data port, each instruction consisting of two bytes. The first 5 bits of the first byte are the command code, and the remaining bits and the second byte are the data. Various controls for character display can be realized by these instructions. MB90092 has 13 kinds of instructions and two kinds of reserved instructions. The specific functions are listed in Table 1.

Table 1 MB90092 instruction set

4 interface circuit with the microcontroller

The connection between the MB90092 and the microcontroller requires only three lines, CS, SCLK, and SIN. Therefore, it only needs to occupy three I/O ports of the microprocessor. Figure 4 shows the connection circuit between MB90092 and ATMEL's AT89S52 microcontroller.

In Figure 4, the chip select signal for MB90092 is provided by P1.1 of the AT89S52, the serial clock is provided by P1.2, and the instructions and data are read from the P1.3 port of the AT89C52. The following is a source code that sends one byte in C:

#include <reg52. h>

#include <absacc. h>

Sbit CLK_A = P1^2;

Sbit DAT_A = P1^3;

Sbit CS_A1 =P1^1;

Void function SendByteA1(byte dataA1)

{

Byte i,n;

i=1;

CLK_A=HIGH;

CS_A1=LOW;

For(n=1;n<=8;n++)

{

DAT_A=dataA1&i;

i<<=1;

_Nop();

CLK_A = LOW;

_Nop();?

_Nop();?

CLK_A=HIGH;

}

CS_A1=HIGH;

}

5 Conclusion

When using the MB90092 chip, you should pay attention to the following points:

(1) To maintain byte synchronization when starting serial data transfer, first set the CS pin high and then deassert.

(2) Before superimposing new characters, you should first release the memory, that is, execute a clear screen command first, otherwise garbled characters and some unexpected displays may occur.

(3) After power-on, the SCLK pin should be forced high before sending serial data.

(4) When designing the printed board, the video trace should be as short and thick as possible, the analog ground and the digital ground should be separated, and only connected at a single point on the power supply to prevent interference.

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