Panasonic KX-FHD333BR, Service Manual

Page: 138 / 196

8.7. MODEM SECTION
8.7.1. FUNCTION
The unit uses a 1 chip modem (IC505) 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. This 1 chip modem (IC505) has hardware which sends and detects all of the necessary signals for FAX communication.
It can be controlled by writing commands from the CPU (IC501: inside ASIC) to the register in the modem (IC505).
This modem (IC505) 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 lines.
Determined in 1968.
Transmission for about 6 minutes at a scanning line density of 3.85 lines/mm.
· Group II (G2)
Using reduction technology in the modulation/demodulation format, an A-4 size document is sent at an official scanning line
density of 3.85 lines/mm for about 3 minutes.
Methods to suppress redundancy are not used.
Determined in 1976.
·
Group III (G3)
Method of suppressing redundancy in the image signal prior to modulation is used. An A-4 size document is sent within
about one minute.
Determined in 1980.
· Group IV (G4)
Transmission is via the data network. A method is provided for suppressing redundancy in signals prior to transmission, and
error-free reception of transmission is possible.
The scope of these facsimile applications is not limited simply to transmission of written statements. Through symbiotic
linkages with other communication methods, it can be expected to expand to include integrated services.
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