AT+i Programmer's Manual - SE Spezial-Electronic AG

28 SerialNET Theory of Operation
28.1 Introduction
SerialNET Theory of Operation
iChip‘s SerialNET mode extends a local asynchronous serial link to a TCP or UDP
socket across a LAN 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 iChip 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 (bidirectional
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 iChip 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
iChip under SerialNET mode routes full-duplex data between a networked terminal and
both types of devices.
28.2 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, iChip is connected to an AT+i aware host.
SerialNET mode can be terminated by: A) applying power to the iChip with the MDSEL
signal pulled low for less than 5 seconds; or, B) issuing the ESC sequence defined as
followed by (+++) (three (+) characters) through the serial port.
When one of these occurs, iChip reboots after terminating SerialNET mode. At this point
iChip reverts to its normal operational mode and again responds to AT+i commands.
28.3 Server Devices
Server devices linger until approached by a remote client. The remote client must know
iChip‘s IP and listening port address in order to establish communications.