Technical information

Chapter 2: AT+i Commands Reference
May 31, 2008 AT+i Commands Reference Manual 2-85
SerialNET Theory of Operation
Introduction
W24's SerialNET mode extends a local asynchronous serial link to a TCP or UDP socket across a
WLAN or Internet. Its main purpose is to allow simple devices, which normally interact over a
serial line, to interact in a similar fashion across a network without requiring any changes in the
device itself. In order to achieve this, SerialNET mode defines a set of associated operational
parameters, which determine the nature of the desired network connection. When W24 is put in
SerialNET mode, it acts as a router between the device's serial port and the network.
Devices that communicate with a terminal over a serial link fall into three major categories:
Output only (i.e. printers), Input only (i.e. controllers) and interactive (bi-directional
communications). The latter are subdivided further into clients and servers. Generally, clients
initiate communications by sending service demands to a server, while servers respond to client
demands.
SerialNET mode reacts differently to client or server devices. When a client device initiates
communications, SerialNET mode must establish a network connection to a remote server before
data may flow between the two systems. On the other hand, when a remote client needs to invoke
a device, the remote client first contacts the W24 and SerialNET is invoked to create a
communication flow to the local server device.
SerialNET mode includes components to handle both server and client local devices. The W24
under SerialNET mode routes full-duplex data between a networked terminal and both types of
devices.
SerialNET Mode
SerialNET mode is established by first defining all related parameters using AT+i commands,
followed by a special Enter SerialNET Mode AT+i command.
Once in SerialNET mode, no additional AT+i commands can be sent, as the host serial link will
be dedicated to raw local-device data. In this mode, auto baud rate is also disabled, since it cannot
be guaranteed that the device will issue an a or A as its first character. Thus, a predefined fixed
baud rate must be specified before switching over to SerialNET mode.
SerialNET mode extends across power-down, since it is assumed that once acting in this mode,
W24 is connected to an AT+i aware host.
SerialNET mode can be terminated by:
• Applying power to the W24 with the MSEL signal pulled low for less than 5 seconds.
• Pulling low the MSEL signal for more than 5 seconds during runtime.
• Issuing the ESC sequence, defined as a half second delay followed by (+++) (three (+)
characters), through the serial port.
When one of these occurs, W24 reboots after terminating SerialNET mode. At this point W24
reverts to its normal operational mode and again responds to AT+i commands.