Ericsson ZAT 19.2 Operation Manual page 302

16. Appendices
16.1.1 Data Communication System
Transmitting of data from a terminal:
e The terminal sends data in the form of digital signals to the modem
« The modem converts (modulates) the digital signals to analogue
signals or tones.
e The receiving modem converts (demodulates) the analogue signals
back to digital.
DIGITAL SIGNALS MODEM ANALOGUE SIGNALS
e The CPU receives the data as binary digits
e The tones are transmitted on the telephone line in similar manner as
human speech
ae
ANALOGUE SIGNALS MODEM DIGITAL SIGNALS
16.1.2 Symbols and bits
When people communicate with each other, they use different
symbols, known as letters and numbers. Computers have only
two symbols available. These symbols are represented by for
instance, a certain voltage present, or no voltage at all, and are
usually denoted binary "1" or binary "0".
Such symbol is cailed a binary digit, or a bit, and represents the
smallest unit of information.
In order to obtain the variety of symbols needed to represent the
known characters, it is necessary to combine a number of digits.
Usually 7 or 8 bits are used in combination. A group consisting
of 8 bits, is called a byte.
Example:
fo {4 Jo [o fo | 1 |1 [1 |
This is a group of eight bits, that represents the character "G".
16-2 LZTR104006 R1.00
Zat 14.4/14.4-7 and 19.2/19.2-7