User's Manual

Table Of Contents
SerialNET Theory of Operation
AT+i Programmer‘s Manual Version 8.32 29-1
29 SerialNET Theory of Operation
29.1 Introduction
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 (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 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.
29.2 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. Similarly, the host interface cannot be determined automatically and
therefore you must set iChip‘s Host Interface to USART0 (HIF=1) or USART1 (HIF=2).
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:
Pulling the MSEL signal low for more than 5 seconds.
Issuing the ESC sequence, defined as a half second delay followed by (+++) (three (+)
characters), over 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.