Xbee SX RS232 RS485 RF Modems

Introduction

These are 1-Watt industrial-grade 900 MHz long range RF modems for wireless cable replacement applications. Digi International’s SX radio technology utilized in the modem provide an RF line-of-sight range (ideal) estimated up to 65 miles. The SX technology provides strong interference blocking which benefits indoor applications in noisy industrial environments. Available interfaces to the modems include RS-232, RS-485, USB, Analog I/O and Digital I/O.

There are two versions available, an RS232/RS485 version (Digi International part# XM-X9-3P-U) and an Analog/Digital I/O version (Digi International part# XM-X9-5P-U). The modem discussed in this article is the RS232/RS485 version, Digi-Key part# 602-1980-ND. Since customers may want to use their own power supply or antenna they are not included with the modems. A separate modem accessory package, Digi-Key part# 602-2109-ND, is available and includes an antenna, power supply, USB cable, RJ45 cable and DB9 adapter.

Since the modems are based on Digi International’s SX wireless modules they are compatible with and can communicate wirelessly with SX modules. The SX modules are available in two RF power variants and two RF output variants. An SX module development kit, Digi International part# 602-1886-ND, is also available. Later in the article, the demonstrations will use communication between an SX modem and an SX module development board in the examples

Hardware

note: see SX RF Modems User Guide for pinout

Network Topologies

These modems are extremely flexible and easy to use. The SX modems can use Digi’s DigiMesh® wireless networking protocol, with redundant mesh network operation and support for low-power sleeping nodes. For applications that don’t require mesh network architecture customers can configure the modem to operate in simple point to point or point to multipoint mode.

XCTU / Configuring the modem

XCTU is a free multi-platform application designed to enable developers to interact with Digi RF modules through a simple-to-use graphical interface. It includes tools that make it easy to set-up, configure and test XBee® RF modules. The XCTU application and USER Guide can be downloaded from https://www.digi.com/products/xbee-rf-solutions/xctu-software/xctu .

Range Test Demonstration Example

Running a range test is a good initial step to perform when setting up devices and testing wireless connectivity between them. Using the range test tool within XCTU makes this very easy to implement and the steps are well documented in the XCTU User Guide. For this demonstration an SX modem is used as the local device and an SX module devlopment board as the remote device. The basic steps are highlighted below:

1 - Start XCTU to find and add the SX modem as LOCAL device

2 - Select Range Test from Tools

3 - In Range Test select LOCAL for local device and click Discover remote devices button

4 - Add remote device and select Start Range Test

Asynchronous Sleep / IO Sampling Demonstration Example

A common design implementation is to use the asynchronous sleep capability of the SX module to save power in battery powered applications. For this demonstration an RS232/485 SX modem is used as the local device and an SX module development board is used as a sleeping node that periodically wales up, uses it’s ADC to sample an analog input pin and sends the value to the local device. The basic steps are highlighted below.

1 - Use XCTU to connect to SX module development board and configure destination address, sleeping mode and I/O sampling

For demonstration:

configure parameters DH and DL to serial# of local device, set SM to 4 for asynchronous cyclic sleep, set D1 to 2 for ADC sampling, set IR to 0x551 for approximate 3 second sample rate

2 - In XCTU, connect to SX modem, switch to Console mode and close serial connection to monitor data received from the sleeping mode

Availability

RS232/RS485 SX Xbee modem ; Digi-Key part# 602-1980-ND ; https://www.digikey.com/products/en?keywords=602-1980-ND

SX Modem accessory package ; Digi-Key part# 602-2109-ND ; https://www.digikey.com/products/en?keywords=602-2109-ND

XBEE SX 900MHZ RF MODULE DEV KIT ; Digi-Key part# 602-1886-ND ; https://www.digikey.com/products/en?keywords=602-1886-ND

Resources

XBee SX RF Modems User Guide XBee RF Modems User Guide

XBee/XBee-PRO SX RF Module User Guide XBee®/XBee-PRO SX RF Module User Guide

XCTU User Guide XCTU User Guide