Canon fax basic 2000 서비스 매뉴얼

G3 FACSIMILE COMMUNICATIONS

5–90

6.2

Signal Types

In G3 facsimile communications, various signals are used in addition to

the previously described binary signals.

(1) Preamble

The preamble is the signal that prefixes the binary signal, and is a series of

the flags for about 1 sec. A “flag” comprises eight bits “01111110” (7E

when expressed in Hex), and the preamble comprises about 37 continuous

flags. Synchronization of the MODEM signals for procedure signals is

performed by prefixing the preamble with binary signals.

(2) Binary signal

Binary signals are signals by which facsimile procedures are handled, and

are obtained by frequency-modulating 1/0. Low-speed signals are used to

prevent transmission errors from occurring at a data transmission speed of

300 bps. The MODEM used at this time uses the modulation system rec-

ommended in 

 recommendation V.21. Binary signals have a function

for checking for errors in the transmitted data.

(3) Image signal

On a G3 facsimile, image signals are coded by coding schemes such as

MH and MR. The image signal modulation system and the transmission

speed differ according to the MODEM in use. Image signals are transmit-

ted at data speeds within the range 2400 bps to 33600 bps. Before image

signals are transmitted, they are prefixed with a “training” signal.

(4) Tonal signal

The sine wave of a determined frequency, in other words a tone, is used as

the tonal signal. This means that the height of the tone has meaning. The

procedure for using this signal is called the “tonal procedure.”

Table 5-13   Signal Types

Type of Signal

Meaning

Preamble signal

Signal prefixed to binary signal

Binary signal

Signal expressed by 0 or 1 to communicate

meaning of procedure

Image signal

Signal of coded image

Tonal signal

Signal  obtained  by giving  meaning  to type  of

tone (frequency)