0 Introduction Character superposition can be widely used in closed circuit television, image systems, car video systems, and highway toll systems. The UPD6453 is NEC's character stacking chip, which makes it easy to design a practical character adder using the chip and simple peripheral circuitry.
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1 UPD6453 performance characteristics UPD6453 can superimpose characters on video usually 12 lines x 24 columns, a total of 288 characters; the displayed character type is 240 characters of English letters, numbers and Japanese that have been solidified in RON and user-defined 16 characters; the character size can be selected from 1 to 4 times; each character can be selected from any of 8 colors: the background of the displayed characters can be selected from any of the background, real background, and square background; character pixels The matrix is ​​in 12×18 mode with no spacing between characters; each character is flashing to control; the data in video RAM can be cleared by power-on or control commands.
2 UPD6453 Control Commands The UPD6453 control commands have three modes, a 1-byte command, a 2-byte command, and a multi-byte command. The 1-byte command and the 2-byte command are both composed of a command part and a data part. All control commands in a multi-byte command use a variable-length serial input mode in 8-bit units; multi-byte commands consist of two or more bytes, which can be input in a simplified mode. Multibyte commands are primarily used for character display. The processing of UPD6453 internal data is in units of each byte input. The control commands of UPD6453 are listed in Table 1, Table 2 and Table 3, respectively.
3 Continuous command input method 1-byte command, 2-byte command or multi-byte continuous command can be input continuously or in combination with other control commands. When controlling the command input, the chip select signal (3rd pin) must be kept low. When a 1-byte command and a 2-byte command are input, the chip select can be kept active at all times. However, when a 1-byte command or a multi-byte command is input after a multi-byte command, the chip select signal must be invalid before being input. If the chip select signal does not have such a change, the UPD6453 treats the incoming 1-byte command and 2-byte command as part of a multi-byte command.
4 Chinese character video overlay The software block diagram of superimposing Chinese characters into video is shown in Figure 1. When superimposing Chinese characters on a video, the dot information of the Chinese characters should be written to the character RAM first.
The UPD6453 chip provides users with 240 character fonts in English, numbers and Japanese, and provides users with an undefined 16-character RAM space. Each font corresponds to an address. For example, the address corresponding to the number 0 is 0x00, the address corresponding to the letter G is 0x10, and the address corresponding to the undefined 16 characters is 0xF0 to 0xFF. Therefore, when writing dot matrix information of a Chinese character to the character RAM, the following steps can be completed:
(1) Set the Chinese character written in the character RAM to be the first Chinese character (the address corresponding to the first Chinese character is 0xF0);
(2) Set the line where the dot matrix information of the Chinese character written in the UPD6453 chip is located (only the dot matrix information of the first line of the Chinese character needs to be set, because the dot matrix information of the character is written in the character RAM) , the line address of the character is automatically added 1);
(3) The dot matrix information of the Chinese character is read from the external character RAM, and the dot matrix information of the Chinese character is written into the character RAM by the "character RAM write data control command".
5 Conclusion This paper introduces the method of superimposing characters on video by using UPD6453 chip. This method is based on the detailed analysis of the characteristics and functions of UPD6453 chip. It has certain guiding significance for applying UPD6453 to realize Chinese character superposition. Because UPD6453 chip has the advantages of simple design, high reliability and good practicability when performing video character superposition, it is a better choice to use UPD6453 to realize Chinese character superposition on video.
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