Technical information

Chapter 2: AT+i Commands Reference
May 31, 2008 AT+i Commands Reference Manual 2-89
e-mail to the RRMA address (if defined) and/or establishes a socket to the address in RRSV (if
defined). The transmission contains the dynamic IP address received from the ISP and its
listening port, on which W24 has an open listening socket, ready to serve the remote client.
W24 goes offline if one of the following events occurs:
• The remote peer closes the SerialNET socket.
• The IATO parameter is defined and times out.
• The terminating string defined in the DSTR parameter is received.
When the optional (!) (Auto-Link mode) flag is specified, W24 immediately goes online in
response to the AT+i!SNMD command, opens the SerialNET listening socket (if it is defined in
the LPRT parameter) or attempts to establish a socket to an HSRn address (if any HSRn is
defined and LPRT is not). In this case, if one of the terminating events occurs, W24 does not go
offline. Rather, the SerialNET socket is closed while W24 stays online and opens the listening or
active socket again, after waiting the SNRD delay.
When the optional (@) (Deferred Connection mode) flag is specified, W24 immediately goes
online in response to the AT+I@SNMD command. It opens the SerialNET listening socket (if it is
defined in the LPRT parameter) but does not attempt to establish a socket to the HSRV address if
it is defined. In this case, if one of the terminating events occurs, W24 does not go offline. Rather,
the SerialNET socket is closed while W24 stays online and opens the listening socket again, after
waiting the SNRD delay.
W24 exits SerialNET mode when one of the Escape procedures is activated.
SerialNET over TELNET
SerialNET over TELNET mode of operation opens a data socket as a TELNET socket, which
allows negotiations of TELNET options over the same socket while the host is sending and
receiving raw data only. This mode partially supports the RFC2217 standard.
SerialNET over TELNET mode is entered by sending the command AT+iSNMD=4 after setting
W24's Host Interface to USART0 (HIF=1) or USART1 (HIF=2).
An error code - I/ERROR (124) - is returned upon setting the SNMD parameter to 4 while the
HIF parameter is not set to either 1 or 2.
Mode of Operation
SerialNET over TELNET mode expands the Auto-Link mode (!SNMD). In this mode, W24
immediately goes online upon activating SerialNET, regardless of whether serial data has arrived
or not.
If the LPRT (Listening Port) parameter is defined, W24 opens a listening port and awaits a
connection, and so it acts as a TELNET server. If, on the other hand, LPRT is not defined, but
HSRV (Host Server) is defined, W24 acts as a TELNET client and immediately opens a TELNET
socket link to the TELNET server.
Note that, even when configured as a client, W24 still acts as a server in RFC2217. See the
following section - "RFC2217 Implementation" - for a more detailed explanation.
The SerialNET over TELNET mode expands W24's TELNET client in the following aspects:
• It allows W24 to operate both as a TELNET server and client.
• It partially supports RFC2217.