课件：数字逻辑3-4(1).ppt

1、Codes for input and displayChapter 3 Design for codes and operation systems Keyboard EncoderEach key control an outputOutput code is one hot code(1 out of 10 code)Keyboard EncoderEach key control two outputsOutput code is two hot code(biquinary code)BCD codesBinary codes for decimal digits (Table 2-

2、9)BCD code：10 Decimal digits,4-bit ASCII code：128 Keyboard signs,7-bit Used for keyboard or display deviceCodes in binary system8421 codeNatural code,just lake 4-bit binary numbers;Each digit is weighted;It has 10 valid code words and 6 invalid code words.BCD codesEach digit is weighted;Self-complem

3、enting;Use MSB to express higher/lower part;It has 10 valid codes and 6 invalid codes.2421 codesBCD codesBCD codesExcess-3 codeIts digit is not weighted;Self-complementing;8421 code+“0011”.Examples:use BCD code for decimal numbers A=19468421 code :A=0001 1001 0100 01102421 code :A=0001 1111 0100 110

4、0Excess-3 code:A=0100 1100 0111 1001 BCD codesKeyboard EncoderKeyboard EncoderCodes in control systemsASCII codes128 Keyboard signs,7-bitComplex pattern displayCodes in control systemsBinary decoder miyi Output equation Codes in control systemsError-detecting codeInformation word+checking bitError-detecting codeInformation word+checking bitError-detecting codeInformation word+checking bitError-detecting codeInformation word+checking bitError-detecting system