M16C Datasheet, PDF (161/262 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

CRC
Preliminary Specifications REV.B
Specifications in this manual are tentative and subject to change.
Mitsubishi microcomputers
M16C / 6N Group
SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER
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 (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 completed
in two machine cycles.
Figure 17-1 shows the block diagram of the CRC circuit. Figure 17-2 shows the CRC-related registers.
Figure 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 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 17-2. CRC-related registers
161
Address
03BE16
When reset
Indeterminate
Values that
can be set
0016 to FF16
RW