AN2120: Connecting an M68HC08 Family Microcontroller to an ...

Application Note
In the on-line state, once a connection has been established with a
modem of a remote system (for instance, an ISP), the local modem
enters the on-line state and no longer attempts to interpret the data
being sent to it. In other words, every data sent while on-line state is
transmitted to the remote modem regardless of its nature. If the remote
system hangs up or for any other reason the carrier signal is lost while
in on-line state, the modem will revert to local command mode.
When the modem receives a command (in command mode), it returns a
result code. This code can be in the form of either a text string or a
numeric code. A numeric code is more appropriate for embedded
systems, but if we want to control the modem by using a terminal and a
keyboard, a verbose mode or text messages are more preferable. We
can set the type of result code by using a command message.
Table 5 shows the result codes of a Hayes-compatible modem.
No.
Verbose
Equivalent
Table 5. Result Codes Summary
0 OK Command executed
1 CONNECT Connection established
2 RING Ring signal detected
Description
3 NO CARRIER Carrier signal lost or not detected
4 ERROR Invalid command, checksum, error in command line,
or command line too long
5 CONNECT 1200 Connection established at 1200 bps
6 NO DIALTONE No dial tone detected
7 BUSY Busy signal detected
8 NO ANSWER No response when dialing a system
9 CONNECT 2400 Connection established at 2400 bps
AN2120
34 MOTOROLA