M16C62N Datasheet, PDF (140/213 Pages) Renesas Technology Corp – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

CRC
Mitsubishi microcomputers
M16C / 62N Group (80-pin)
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 1.17.1 shows the block diagram of the CRC circuit. Figure 1.17.2 shows the CRC-related registers.
Figure 1.17.3 shows the calculation example using the CRC calculation circuit
Data bus high-order bits
Data bus low-order bits
Eight low-order bits
Eight high-order bits
CRC data register (16)
CRC code generating circuit
x¹⁶ + x¹² + x⁵ + 1
(Addresses 03BD16, 03BC16)
CRC input register (8) (Address 03BE16)
Figure 1.17.1. Block diagram of CRC circuit
CRC data register
(b15)
b7
(b8)
b0 b7
b0
Symbol
CRCD
Address
When reset
03BD16, 03BC16 Indeterminate
Function
CRC calculation result output register
Values that
can be set
RW
000016 to FFFF16
CRC input register
b7
b0
Symbo
CRCIN
Data input register
Function
Figure 1.17.2. CRC-related registers
Address
03BE16
When reset
Indeterminate
Values that
can be set
0016 to FF16
RW
139