Canon fax basic 2000 サービスマニュアル

FACSIMILE SYSTEM

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5. FLOW OF IMAGE SIGNALS

5.1

Transmission

(1) Images are read by the contact sensor, and the resulting analog image

data is sent to the SCNT board.

(2) The analog image data that arrives from the contact sensor undergoes

digital image data conversion, error diffusion processing or other pro-

cessing on the image processor IC of the reading control section. The

resulting image data is sent to the system controller by serial commu-

nications.

(3) The system controller converts the digital image data from serial to

parallel and writes the data to DRAM.

In memory transmission mode, the 

 codes the digital image data

in DRAM by the 

, and writes the resulting data to DRAM

again.

(4) In the memory transmission mode, the coded digital image data is con-

verted to raw data on the MPU. After this, coding according to the

transmission mode is performed, and the resulting data is written to

buffer area in DRAM.

In the direct transmission mode, the MPU codes the raw data in

DRAM matched to the transmission mode, and writes the resulting

data to buffer area in DRAM.

(5) The MPU transfers the data in DRAM buffer area to the MODEM one

byte at a time in response to requests from the MODEM. When the

data arrives, the MODEM performs modulation.

(6) After the data has been modulated, it is amplified by the 2-wire/4-wire

conversion circuit on the NCU board, and is sent to the telephone line

from L1 and L2.