KX-FL423RU - Panasonic Fax Service Manual (repair manual). Page 26

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6. Explanation of Communication and Compression Technology

a. G3 Communication Signals (T. 30 Binary Process) 

For G3 Facsimile communication, this is the procedure for exchanging control signals between the sending and receiving
machines both before and after transmission of image signals.
Control signals at 300 bps FSK are: 1850 Hz...0, 1650Hz...1. 
An example of a binary process in G3 communication is shown below.

Explanation of Signals 
Control signals are comprised mainly of 8-bit identification signals and the data signals added to them. Data signals are
added to DIS and DCS signals.
Signal.....DIS (Digital Identification Signal) 
Identification Signal Format.....00000001
Function:
Notifies the capacity of the receiving unit. The added data signals are as follows.

Signal.....DCS (Digital Command Signal) 
Identification Signal Format.....X1000001

Example
 (Some models do not support the following items.):

Bit No.

DIS/DTC

DCS

1

Transmitter --- T.2 operation

2

Receiver --- T.2 operation

Receiver --- T.2 operation

3

T.2 IOC = 176

T.2 IOC = 176

4

Transmitter --- T.3 operation

5

Receiver --- T.3 operation

Receiver --- T.3 operation

6

Reserved for future T.3 operation features

7

Reserved for future T.3 operation features.

8

Reserved for future T.3 operation features.

9

Transmitter --- T.4 operation