M30622ECTFP datasheet(159/184 Pages) MITSUBISHI

159 / 184 page

159

Tentative Specifications REV.A

Mitsubishi microcomputers

M16C / 62T Group

SINGLE-CHIP 16-BIT CMOS MICROCOMPUTER

Specifications in this manual are tentative and subject to change.

Under

development

CRC

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 1.22.1 shows the block diagram of the CRC circuit. Figure 1.22.2 shows the CRC-related registers.

Figure 1.22.3 shows the calculation example using the CRC calculation circuit

Figure 1.22.2. CRC-related registers

Symbol

Address

When reset

CRCD

03BD16, 03BC16

Indeterminate

b0 b7

(b15)

(b8)

CRC data register

CRC calculation result output register

Function

Values that

can be set

000016 to FFFF16

Symbo

Address

When reset

CRCIN

03BE16

Indeterminate

CRC input register

Data input register

Function

Values that

can be set

0016 to FF16

Eight low-order bits

Eight high-order bits

Data bus high-order bits

Data bus low-order bits

CRC data register (16)

CRC input register (8)

CRC code generating circuit

x16 + x12 + x5 + 1

(Addresses 03BD16, 03BC16)

(Address 03BE16)

Figure 1.22.1. Block diagram of CRC circuit

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