M30218 Datasheet, PDF (127/179 Pages) Mitsubishi Electric Semiconductor – M30218 Group

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CRC Calculation Circuit
Mitsubishi microcomputers
M30218 Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
CRC Calculation Circuit
The Cyclic Redundancy Check (CRC) calculation circuit detects an error in data blocks. The microcom-
puter uses a generator polynomial of CRC_CCITT (X¹⁶ + X¹² + X⁵ + 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 CRC
code is set in a CRC data register each time one byte of data is transferred to a CRC input register after
writing an initial value into the CRC data register. Generation of CRC code for one byte of data is com-
pleted in two machine cycles.
Figure UC-1 shows the block diagram of the CRC circuit. Figure UC-2 shows the CRC-related registers.
Figure UC-3 shows the calculation example using the CRC calculation circuit
Data bus high-order bits
Data bus low-order bits
Eight low-order bits
CRC data register (16)
CRC code generating circt
x¹⁶ + x¹² + x⁵ + 1
Eight high-order bits
(Addresses 03BD16, 03BC16)
CRC input register (8) (Address 03BE16)
Figure UC-1. Block diagram of CRC circuit
CRC data register
(b15)
b7
(b8)
b0 b7
Symbol
b0
CRCD
Address
When reset
03BD16, 03BC16 Indeterminate
Function
CRC calculation result output register
Values that _{R W}
can be set
000016 to FFFF16
CRC input register
b7
b0
Symbo
CRCIN
Data input register
Function
Figure UC-2. CRC-related registers
126
Address
03BE16
When reset
Indeterminate
Values that
can be set
0016 to FF16
RW