CHAPTER 24 SAFETY FUNCTIONS
Page 780 of 920
24.3.2
CRC operation function (general-purpose CRC)
In order to guarantee safety during operation, the IEC61508 standard mandates the checking of data even while
the CPU is operating.
In the RL78/G1H, a general CRC operation can be executed as a peripheral function while the CPU is operating.
The general CRC can be used for checking various data in addition to the code flash memory area. The data to
be checked can be specified by using software (a user-created program). In HALT mode, the CRC operation
function can be used only during DTC transfer.
The general CRC operation can be executed in the main system clock operation mode as well as the subsystem
clock operation mode.
The CRC generator polynomial used is “X
16
+ X
12
+ X
5
+ 1” of CRC-16-CCITT. The data to be input is inverted in
bit order and then calculated to allow for LSB-first communication. For example, if the data 12345678H is sent
from the LSB, values are written to the CRCIN register in the order of 78H, 56H, 34H, and 12H, enabling a value
of 08F6H to be obtained from the CRCD register. This is the result obtained by executing a CRC operation on the
bit rows shown below, which consist of the data 12345678H inverted in bit order.
Caution
Because the debugger rewrites the software break setting line to a break instruction during
program execution, the CRC operation result differs if a software break is set in the CRC
operation target area.
CRCIN setting data
78H
56H
34H
12H
Bit representation data
0111 1000
0101 0110
0011 0100
0001 0010
Bit reverse
Bit reverse data
0001 1110
0110 1010
0010 1100
0100 1000
Operation with polynomial
Result data
0110 1111
0001 0000
Bit reverse
CRCD data
0000 1000
(08F6H)
1111 0110
←
Obtained result
Summary of Contents for RL78/G1H
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