Z02215 Datasheet, PDF (19/74 Pages) Zilog, Inc. – Single Chip Modem with Integrated Controller, Data Pump, and Analog Front End

Z02215
Single Chip Modem with Integrated Controller, Data Pump, and AFE
13
ON-LINE
After successfully completing Handshaking the modems enter the ON-LINE state.
When a modem is in the ON-LINE state, data received from its terminal is sent
over the telephone line to the other modem. Data received from the other modem
is sent to the terminal.
COMMAND
If the terminal sends a special escape sequence to a modem in the ON-LINE
state, the modem enters the COMMAND state. During COMMAND state the
modem maintains the connection with the other modem but does not pass data
between the terminal and the other modem. Instead, data received from the termi-
nal is treated as AT commands in the same way as if the modem was in the Idle
state. The modem can be returned to the ON-LINE state by the O command. Data
received from the other modem while a modem is in COMMAND state is dis-
carded unless the modem can buffer it for display on the terminal when the
modem re-enters the ON-LINE state.
Retrain
During a telephone line connection, the modem tries to remain synchronized with
the remote modem by adapting to changes in telephone line connection and
bridging transient noises such as call waiting, analog switching and cross talk. In
V.22bis and higher speed data modes, if the modem loses synchronization with
the remote modem data can not be received until synchronization is restored by a
process called Retraining. During Retraining the modem accepts data and com-
mands from the terminal but does not transmit data to, or receive data from, the
other modem.
AT Command Set
Command lines are typed to the modem from the terminal when the modem is in
the IDLE or COMMAND state. The modem does not execute any of the com-
mands in a command line until after the command line is ended by the end-of-line
character <CR>. A command line is a string of characters starting with the A and T
characters and ending with a special end-of-line character, <CR>. Characters
typed before the AT are ignored. Command lines contain, at most, 40 characters
after the AT. The modem does not execute any of the commands in a command
line that is too long.
To echo command line characters, use the E1 command.
PS001907-0904
AT Command Set