7.3.4. MODEM SECTION
7.3.4.1. FUNCTION
The unit uses CODEC (IC609) and ASIC (IC604) that serves as an interface between the control
section for FAX transmission and reception and the telephone line. During a transmitting
operation, the digital image signals are modulated and sent to the telephone line.
During a receiving operation, the analog image signals which are received via the telephone line
are demodulated and converted into digital image signals. The communication format and
procedures for FAX communication are standardized by ITU-T. CODEC and ASIC has hardware
which sends and detects all of the necessary signals for FAX communication.
It can be controlled by writing commands from the CPU (IC604: inside ASIC).
This CODEC and ASIC also sends DTMF signals, generates a call tone (from the speaker), and
detects a busy tone and dial tones.
Overview of Facsimile Communication Procedures (ITU-T Recommendation):
1. ON CCITT (International Telegraph and Telephone Consultative
Committee)
The No. XIV Group of ITU-T, one of the four permanent
organizations of the International Telecommunications Union
(ITU), investigates and make recommendations on international
standards for facsimiles.
2. Definition of Each Group
- Group I (G1)
Official A-4 size documents without using formats which
reduce the band width of a signal are sent over telephone
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