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XE900SL10

Smart Spread Spectrum Transceiver

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XE900S-500 COMMUNICATIONS CONTROLLER

Configuring the XE900S-500 for Sensor Operation

All SensorOnAir control functions for the analog inputs

and digital I/O’s are performed by the communications

controller within the XE900S-500. Modem-like AT

commands loaded through the serial interface, program

the functions of the analog and digital I/O lines. The AT

commands used to program the SensorOnAir functions

are then stored in the XE900S-500 Flash memory. This

allows the XE900S-500 to be first programmed and then

installed in the application. The communications

controller uses the information stored in Flash memory to

control the analog and digital I/O lines.

SensorOnAir Commands™

Below is a list of the AT commands used to program the

direct control of sensors using the communications

controller in the XE900S-500.

S107 -

Defines the function of the programmable I/O lines.

The two analog input lines, ADC0 and ADC1, can

also be defined as digital I/O lines if needed. The four

programmable digital I/O lines, DIO0, DIO1, DIO2,

and DIO3; can be set as either inputs or outputs. The

value of this command is stored in flash memory within

the XE900S-500.

AT&IAn? - This command allows a local host to read the value

of Analog Input “n.”

AT&IDn? - This command allows a local host to read the

status of Digital I/O “n.”

AT&IDn=z - This command allows a local host equipment to

set the condition of the local digital output “n.” When

z=0 the output is set to a logic low; when z=1 the

output is set to a logic high.

AT#IxxxAn? - This command allows the value of Analog Input

“n” on node address “xxx” to be read remotely.

AT#IxxxDn? - This command allows the status of Digital I/O

“n” on node address “xxx” to be read remotely

AT#IxxxDn=z - This command allows the condition of the

local digital output “n” on node address “xxx” to be

set remotely. When z=0 the output is set to a logic

low; when z=1 the output is set to a logic high.

WIRELESS COMMUNICATIONS

The communications controller manges the RF Link. This

includes the frequency hopping algorithm for spread

spectrum operation; collision avoidance, node

addressing, and packetizing data. The communications

controller allows support for point-to-point, point-to-

multipoint or multipoint networks.

Carrier Sense Multiple Access (CSMA)

To prevent collisions between network nodes the

XE900S-500 uses a Carrier Sense Multiple Access protocol

for each network transceiver. In normal communications

all nodes, including the Master node in a point-to-

Multipoint network, listen for communications activity

before initiating a session. If a wireless link already exists,

the transceiver waits until that session is complete before

initiating a wireless link.

Data Packets

All data presented by the system host is placed into

packets by the XE900S-500 communications controller

for transmission across the wireless link. These packets

provide addressing and error correction for the wireless

communications. The communications controllers place

the data in packets only for the wireless link. The data is

extracted from the packets before being sent out the serial

interface.

File Transfer Mode

Xecom’s XE900S-500 incorporates a File Transfer mode

that uses a simplified networking protocol so that the

maximum data transfer rate is achieved. In this mode the

XE900S-500 does not automatically retransmit blocks

containing errors. A CRC 16 checksum is calculated,

transferred at the end of the file, and checked by the

receiving unit. An “ERROR” message is displayed if the

checksum calculated at the receive end does not match

the checksum transmitted with the data.

The File Transfer Mode is controlled by the AT#T

command. The format of the command is AT#Txx; where

xx is the destination address of the file. Following is a

sample file transfer.

XECOM

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XE900S-500

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