Crc Calculation Circuit; Overview; Crc Calculation Circuit-Related Registers; Operation - Renesas M16C Series User Manual

M30240 Group

2.8 CRC Calculation Circuit

2.8.1 Overview

The Cyclic Redundancy Check (CRC) calculation circuit is used to detect errors in data blocks. The
calculation method compares CRC code formed from transmission data by use of a polynomial
generator with CRC check data to detect errors in transmission data. Using the CRC calculation circuit
allows generation of CRC code. A polynomial counter is used for the polynomial generation of
16
CRC_CCITT (X + X

2.8.1.1 CRC calculation circuit-related registers

Figure 2.107 shows the memory map of CRC-related registers, and Figure 2.108 shows CRC-related
registers.
Figure 2.107: Memory map of CRC-related registers
CRC data register
(b15)
b7
CRC input register
b7
Figure 2.108: CRC-related registers

2.8.2 Operation

The following describes the operation of CRC calculation. Figure 2.109 shows an example of the CRC
calculation circuit using data 0123
(1) The CRC calculation circuit sets an initial value in the CRC data register.
(2) Writing 1 byte of data to the CRC input register generates CRC code based on the data register.
CRC code generation for 1 byte of data finishes in two machine cycles.
(3) The CRC calculation circuit detects an error by means of comparing the CRC-checking data with
the content of the CRC data register, after the next byte of data is written to the CRC input register.
(4) The content of the CRC data register becomes the CRC code after all data is written.
Rev.1.00 Sep 24, 2003 Page 263 of 360
12 5
+ X + 1).
03BC
16
CRC data register (CRCD)
03BD
16
03BE CRC input register (CRCIN)
16
(b8)
Symbol
b0 b7 b0
CRCD
Function
CRC calculation result output register
b0 Symbo
CRCIN
Function
Data input register
.
16
Address When reset
03BD , 03BC Indeterminate
16 16
Values that
R
can be set
0000 to FFFF
16 16
Address When reset
03BE Indeterminate
16
Values that
R
can be set
00 to FF
16 16
CRC Calculation Circuit
W
W