Crc Calculation Circuit - Renesas M16C Series User Manual

M30240 Group

1.2.25 CRC Calculation Circuit

The Cyclic Redundancy Check (CRC) calculation circuit detects an error in data blocks. The
microcomputer uses a generator polynomial of CRC_CCITT (X
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
completed in two machine cycles.
Figure 1.104 shows the block diagram of the CRC circuit. Figure 1.105 shows the CRC-related registers.
Figure 1.104: Block diagram of CRC circuit
CRC data register
(b15)
b7
CRC input register
b7
Figure 1.105: CRC-related registers
Rev.1.00 Sep 24, 2003 Page 109 of 360
Data bus high-order bits
Data bus low-order bits
Eight low-order bits
CRC data register (16)
CRC code generating circuit
16 12
x + x
CRC input register (8)
(b8)
Symbol
b0 b7 b0
CRCD
Function
CRC calculation result output register
b0 Symbo
CRCIN
Function
Data input register
16 12
+ X + X
Eight high-order bits
(Addresses 03BD
5
+ x + 1
(Address 03BE )
16
Address When reset
03BD , 03BC Indeterminate
16 16
Values that
can be set
0000
16
Address When reset
03BE Indeterminate
16
Values that
can be set
00
16
CRC Calculation Circuit
5
+ 1) to generate CRC code.
, 03BC )
16
16
R W
to FFFF
16
R W
to FF
16