M16C User Manual.pdf

CRCMitsubishi microcomputersM16C / 62 GroupSINGLE-CHIP 16-BIT CMOS MICROCOMPUTERCRC Calculation CircuitThe Cyclic Redundancy Check (CRC) calculation circuit detects an error in data blocks. The microcomputeruses a generator polynomial of CRC_CCITT (X 16 + X 12 + X 5 + 1) to generate CRC code.The CRC code is a 16-bit code generated for a block of a given data length in multiples of 8 bits. The CRCcode is set in a CRC data register each time one byte of data is transferred to a CRC input register afterwriting an initial value into the CRC data register. Generation of CRC code for one byte of data is completedin two machine cycles.Figure 1.22.1 shows the block diagram of the CRC circuit. Figure 1.22.2 shows the CRC-related registers.Figure 1.22.3 shows the calculation example using the CRC calculation circuitData bus high-order bitsData bus low-order bitsEight low-order bitsEight high-order bits CRC data register (16)CRC code generating circuitx 16 + x 12 + x 5 + 1CRC input register (8) (Address 03BE16)(Addresses 03BD16, 03BC16)Figure 1.22.1. Block diagram of CRC circuitCRC data register(b15)(b8)b7 b0 b7 b0Symbol Address When resetCRCD 03BD16, 03BC16 IndeterminateFunctionCRC calculation result output registerValues thatcan be set000016 to FFFF16R WCRC input registerb7b0Symbo Address When resetCRCIN 03BE16 IndeterminateData input registerFunctionValues thatcan be set0016 to FF16R WFigure 1.22.2. CRC-related registers165