Canon fax basic 2000 サービスマニュアル

5–121

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G3 FACSIMILE COMMUNICATIONS

The following shows the function of the respective bytes.

What Is The “Frame Checking Sequence (FCS)”

The “FCS” is a sequence that checks whether there are any transmission

errors in the frame. FCS is a 2-byte code.

The following briefly describes how the FCS operates.

(1) During transmission of frames, a specific computation is performed on

the content from A (address field) through to FIF (facsimile informa-

tion field) at the transmitting side. The results of that computation is

always expressed as a 2-byte code.

(2) The result of (1) is inserted in FCS (Frame Check Sequence) and

transmitted.

(3) On the receiving side, the reverse computation to that in (1) is exe-

cuted from the address field to the FCS during frame reception.

(4) If the result is equal to a certain value, it can be known that the frame

is free of transmission errors.

This kind of transmission error detection method is called the Cyclic

Redundancy Check (CRC).

Table 5-18   Content of FIF of NSF, NSC and NSS

Byte

Content

1st and 

2nd bytes

ITU-T 

members’ codes

Code which indicates the nationality

of the manufacturer.

Japan: All bits “0”

3rd byte

Maker code

Code which indicates the name of

the manufacturer.

Canon code is 88H. (See Appendix

From 

the 4th byte 

onwards

Free area

Manufacturers can freely use this

area. The contents of other manufac-

turers are unknown.

At Canon, information such as the

“user’s name” and “non-standard

functions” is entered.