Microhard Systems 99P2 User Manual

Operating Manual

900 MHz Wireless

Spread-Spectrum OEM Modem

Revision 03 - May 12, 1999

Microhard Systems Inc. has made every effort to assure that this document is accurate and complete. However, the
company reserves the right to make changes or enhancements to the manual and/or the product described herein at
any time and without notice. Furthermore, Microhard Systems Inc. assumes no liability resulting from any omissions
in this document, or out of the application or use of the device described herein.

Microhard Systems Inc.

Leaders in Wireless Telecom

Contents

1. Introduction

1.0 Product Overview ........................................................................................................................................................ 1

1.1 Features........................................................................................................................................................................ 1

1.2 About this Manual ....................................................................................................................................................... 2

2. Initial Setup and Configuration

2.0 Unpacking and Inspection............................................................................................................................................ 3

2.1 Additional Requirements ............................................................................................................................................. 3

2.2 Connectors and Indicators ........................................................................................................................................... 3

2.3 Configuration............................................................................................................................................................... 5

2.4 Checking the Link......................................................................................................................................................... 6

3. Configuration Options

3.0 Command Line Interface.............................................................................................................................................. 7

3.1 AT Commands............................................................................................................................................................. 8

A - Answer.................................................................................................................................................................... 8

D - Dial........................................................................................................................................................................ 8

E - Command Echo...................................................................................................................................................... 8

I - Identification........................................................................................................................................................... 8

O - Online Mode.......................................................................................................................................................... 8

Q - Quiet Mode............................................................................................................................................................ 9

V - Result Codes Display............................................................................................................................................. 9

W - Connection Result................................................................................................................................................. 9

Z - Reset Modem and load stored configuration.......................................................................................................... 9

&C - DCD (Data Carrier Detect) ................................................................................................................................. 9

&D - DTR (Data Terminal Ready)............................................................................................................................... 9

&F - Load Factory default configuration..................................................................................................................... 9

&K - Handshaking........................................................................................................................................................ 9

&S - DSR (Data Set Ready)....................................................................................................................................... 10

&V - View Configuration........................................................................................................................................... 10

&W - Write Configuration to memory....................................................................................................................... 10

Sxxx? - Read S register value .................................................................................................................................... 10

Sxxx=yyy - Set S register value ................................................................................................................................. 10

3.2 Command Result Codes............................................................................................................................................. 10

3.3 S Registers ................................................................................................................................................................. 11

S Register 2 - Escape Code......................................................................................................................................... 11

S Register 3 - CR Control Code................................................................................................................................. 11

S Register 4 - Linefeed Control Code........................................................................................................................ 11

S Register 5 - Backspace Control Code..................................................................................................................... 11

S Register 101 - Operating Mode .............................................................................................................................. 12

S Register 102 - Serial Baud Rate.............................................................................................................................. 13

S Register 103 - Wireless Link Rate.......................................................................................................................... 14

S Register 104 - Network Address............................................................................................................................. 14

S Register 105 - Unit Address.................................................................................................................................... 14

S Register 106 - Hopping Pattern .............................................................................................................................. 14

S Register 107 - Encryption Key ............................................................................................................................... 14

S Register 108 - Output Power Level ........................................................................................................................ 15

S Register 109 - Hopping Interval ............................................................................................................................. 16

S Registers 111 to 113 - Packet Parameters - Point to Point Mode............................................................................ 16

S Registers 111 to 115 - Packet Parameters - Point to Multipoint Mode................................................................... 17

Appendices

A. Modem Command Summary ............................................................................................................................. 19

B. Serial Interface................................................................................................................................................... 21

C. Sample Schematic Diagram ............................................................................................................................... 23

D. Modem Setup Overview .................................................................................................................................... 25

E. Technical Specifications.................................................................................................................................... 27

F. Glossary ............................................................................................................................................................. 29

MHX-900 Operating Manual: Contents i

1. Introduction

1.0 Product Overview

Congratulations on choosing the MHX-900 wireless modem module! Your
new MHX-900 modem is a state-of-the-art, 900 MHz frequency-hopping
spread-spectrum communications transceiver module. When the MHX-900
module is incorporated into the design of new or existing equipment, terminal
devices (DTEs) up to 30 km (or more)1 apart will be capable of establishing
high-speed2 communications wirelessly.

MHX-900 modules provide a practical and reliable alternative to using
traditional analog phone-line modems or “permanent wire” serial cable
(RS-232) connections for data communications between terminal equipment.
Moreover, wireless data communications using the MHX-900 module means
you will benefit from:

n greater flexibility and freedom to relocate terminal equipment,
n eliminated requirement for access to wire-based transfer media

such as telephone lines,

n the ability to communicate through walls, floors, and many

other obstacles.

While the MHX-900 module is compact in its design, it delivers power and
convenience and offers quality and dependability. The MHX-900 module’s
versatility makes it the ideal solution for applications ranging from office­productivity to industrial data control and acquisition.

While a pair of MHX-900 modules can link two terminal devices (“point-to­point” operation), multiple MHX-900 modules can be used together to create
a network of various topologies (“point-to-multipoint” operation). Multiple
independent networks can operate concurrently, so it is possible for unrelated
communications operations to take place in the same or a nearby area without
sacrificing privacy, functionality, or reliability.

1.1 Features

Key features of the MHX-900 module include:

n transmission within a public, license-exempt band of the radio

spectrum3 – this means there are no conditions on usage of the
MHX-900 module, and that it can be used without restrictions
or access fees (such as those incurred by cellular airtime);

n a serial I/O data port (TTL levels) with handshaking and

hardware flow control, allowing the MHX-900 module to inter­face directly to any microprocessor with an asynchronous serial
interface.

1

Ideal conditions with clear line-of-sight communications, using high-gain antennas.

2

Up to 115,200 bits per second (bps).

3

902-928 MHz, which is license-free within North America; may need to be factory-configured
differently for some countries.

MHX-900 Operating Manual: Chapter 1 Introduction. 1

n twenty different user-selectable pseudo-random hopping

patterns to offer the possibility of separately operating multiple
networks while providing security, reliability and high tolerance
to interference;

n encryption key with 65536 user-selectable values to maximize

security and privacy of communications;

n built-in CRC-16 error detection and auto re-transmit to provide

100% accuracy and reliability of data;

n ease of installation and use – the MHX-900 module uses a

subset of standard AT style commands making it compatible
with most communication packages, such as HyperTerminal.

While the typical application for the MHX-900 is to provide a mid- to long­range wireless communications link between DTEs, it can be adapted to
almost any situation where an asynchronous serial interface is used and data
intercommunication is required.

1.2 About this Manual

This manual has been provided as a guide and reference for installing and
using MHX-900 wireless modem modules. The manual contains instructions,
suggestions, and information which will help you set up and achieve optimal
performance from your equipment using the MHX-900 module.

It is assumed that users of the MHX-900 module have either system
integration or system design experience. Chapter 2 details the requirements
and connections of the MHX-900 module. Chapter 3 describes the AT
command register setup and configuration. The Appendices, including the
Glossary of Terms, are provided as informational references which you may
find useful throughout the use of this manual as well as during the operation
of the wireless modem.

Throughout the manual, you will encounter not only illustrations that further
elaborate on the accompanying text, but also several symbols which you
should be attentive to:

Caution or Warning: Usually advises against some action which could
result in undesired or detrimental consequences.

Point to Remember: Highlights a key feature, point, or step which is worth
noting, Keeping these in mind will make using the MHX-900 more useful
or easier to use.

Tip: An idea or suggestion is provided to improve efficiency or to make
something more useful.

With that in mind, enjoy extending the boundaries of your communications
with the MHX-900 module.

2 MHX-900 Operating Manual: Chapter 1 Introduction

2. Initial Setup and Configuration

2.0 Unpacking and Inspection

The following items should be found in the shipping carton. Inspect the
contents for any shipping damage. Report damages or shortages to the
distributor from which the unit was purchased. Keep all packing materials in
the event that transportation is required in the future.

Package contents (normal distribution):

1 MHX-900 Wireless Modem module 1
2 Operating Manual (this document) 1

2.1 Additional Requirements

Since the MHX-900 module is a unique product in a class of its own, it will
communicate only with another MHX-900 module which has been
compatibly configured. Thus, at least two MHX-900 modules will be
required to establish a wireless communications link.

Additionally, the following requirements should be taken into consideration
when preparing to incorporate the MHX-900 module in new or existing
designs.

n Relatively small footprint for the MHX-900 module (e.g., 2.1”

W x 3.5” L x 0.8” H) on the OEM PCB.

n Serial port and control signals from the host microprocessor.

See sample application schematics in Appendix C.

n +5 Vdc supply from the host OEM electronics (+ 10%).
n An external antenna (customer supplied).

2.2 Connectors and Indicators

The MHX-900 module connects to the host equipment by a dual row header
on the underside of the unit. This enables the MHX-900 module to be
directly soldered onto the host equipment manufacturer’s PCB.

The MHX-900 radio deck is attached via a 40 pin header soldered directly to
the PCB. The radio deck also has an antenna connector. A suitable antenna
must be used to ensure adequate performance of the MHX-900 module.

The MHX-900 module is equipped with status LEDs which show the current
operating mode for the unit. The LED signals also are also brought out to
external connectors to be monitored by the OEM microprocessor.

The output drive capability of any output signal pin is approx. 5 mA.
The pin description and location of the MHX-900 is shown on the following

page.

MHX-900 Operating Manual: Chapter 2 Initial Setup and Configuration 3

Top View

Tx Mode LED

Rx Mode LED

For maximum power, use
separate power supplies for
the radio and the digital
electronics.

For OEM design simplicity,
connect both the radio and
logic VCC connections
together. This saves a
regulated power supply.

Caution: Using any other power
supply which does not provide the
proper voltage or current could
damage the MHX-900 module.

Vcc Radio
Vcc Radio
Vcc Logic
Vcc Logic
Vcc Logic
Vcc Logic
Vcc Logic

N/C

/CONFIG

/RESET

GND
GND
GND
GND
GND
GND
GND
N/C
N/C
N/C

1

20

Antenna Connector

40

21

N/C
N/C
N/C
N/C
N/C
N/C
N/C

RSSI LED 3
RSSI LED 2
RSSI LED 1
CTS
RTS
DSR
N/C
DTR
TxD
RxD
DCD

The interface connectors and indicator lights are summarized below:

Vcc Radio - These connections supply power for the MHX-900 module’s radio

deck electronics. For 1 watt maximum output, the required supply rating
should be 5.25 VDC +- 5%. Limiting this to 5.0 Vdc will limit the output
power slightly. Required current depends on transmit duration and output
power. Maximum current at full transmit power is 600 mA DC.

Vcc Logic - These connections supply power for the MHX-900 module’s digital

electronics. To simplify the OEM design, the Radio VCC can be
connected to the Logic VCC. Maximum current while transmitting is
approx. 100 mA DC.

GND - These are the Ground supply connections for the digital and radio

electronics.

/RESET - This momentary active low input signal (100 ms typical) resets the

digital electronics.

/CONFIG - Leave this pin unconnected. Do NOT ground.
Receive Signal Strength Indicator (RSSI) LEDs - These outputs show the

quality/strength of the received signal. As the signal strength increases,
the number of active outputs increase incrementally.

Data Port (DCE) - Pins 21 through 28 inclusive. This port is used to interface

the MHX-900 module to a DTE device and operates at 2400 to 115,200
bps. The same port is used to configure the modem by interfacing to the
host microprocessor. See Appendix B for details on the serial interface
signals.

RX Mode LED - This active low output indicates when the modem receives data

over the wireless link, as well as during internal carrier search and
synchronization operations.

TX Mode LED - This active low output indicates that the modem is transmitting

data wirelessly. This light flashes during initial startup and carrier
synchronization.

Antenna Connector - The antenna is attached to this connection.
N/C - These pins are reserved for future use. Do not connect to this pins.

4 MHX-900 Operating Manual: Chapter 2 Initial Setup and Configuration

2.3 Configuration

Prior to establishing a wireless link, each MHX-900 module that will
participate in the link must be correctly configured for compatibility and for
the desired mode of operation.

The two most common types of networks used are:

n Point-to-point: A Master station communicates with a single

Slave station.

n Point-to-multipoint: A Master station communications with

two or more Slave stations.

Within any network, the Master will communicate only with Slave(s)
assigned to the same network. Similarly, a Slave will only communicate with
the Master of the network to which it is assigned.

2.3.1 Quick Start Approach

The minimum configuration requirements for point-to-point and point-to­multipoint are summarized below. These requirements will get you started

and only ensure that a link can be established, but do not necessarily provide
the best performance; optimization of the communications link is discussed

in later sections.

A. Point-to-Point

To establish a point-to-point communications link, the following requisites
must be satisfied:

n The Operating Mode for one modem must be configured as a

“Master - Point-to-Point”, and the other as a “ Slave - Point-to­Point”.

n The Wireless Link Rate for both modems must be the same.
n The Network Address assigned for both modems must be the

same.

n The Unit Address assigned for both modems must be the same.
n The same Hopping Pattern must be selected for both modems.
n The same Hopping Interval must be selected for both modems.
n Both modems must use the same Encryption Key.

MHX-900 Operating Manual: Chapter 2 Initial Setup and Configuration 5

B. Point-to-Multipoint

To establish a point-to-multipoint network, the following requisites must be
satisfied:

n The Operating Mode for one modem must be configured as a

Point-to-Multipoint Master, and the others as Point-to­Multipoint Slaves.

n The Wireless Link Rate for all modems must be the same.
n The Network Address assigned to all modems must be the same.
n Each Slave must be assigned a unique Unit Address (Unit Address

0 is not supported).

n The same Hopping Pattern must be selected for all modems.
n The Hopping Interval is determined by the Master modem, and is

therefore configured only at the Master.

n All modems must use the same Encryption Key.

Each of the parameters above are defined by specific S registers. Settings are
not immediately stored in non-volatile memory. The command &W writes
the current configuration into non-volatile memory, and are therefore retained
even after powering down. Each item and the settable parameters within the
modem configuration are described in detail in Chapter 3: Configuration
Options.

2.4 Checking the Link

Warning: Using an antenna that
is inappropriate for use with the
MHX-900 module could result in
undesired performance, and may
damage the unit. It is the user’s
responsibility to ensure the
antenna has adequate lightning
protection.

Once configured properly, a pair or set of communicating modems can be tested

to ensure that a link can be successfully established. Connect an appropriate
antenna to each MHX-900 module. The modems should indicate the status of

the wireless link via the RSSI outputs on each unit:
If the link is good, up to three RSSI outputs should be active; and if the link

is absent (due to a fault at one end or another, such as misconfiguration), the
outputs will be inactive.

It is recommended that if MHX-900 modules will be deployed in a field
where large distances separate the units, the modems should be configured
and tested in close proximity (e.g., in the same room) first to ensure a good
link can be established and settings are correct. This will facilitate
troubleshooting, should problems arise. In a multipoint system, only the
Slave modems give valid RSSI readings.

Microhard Systems Inc. provides a development system which supplies all
system power and RS-232 level shifting circuits required to connect a MHX­900 module to a PC. This can serve as an invaluable aid in OEM system
design.

6 MHX-900 Operating Manual: Chapter 2 Initial Setup and Configuration

3. Configuration Options

3.0 Command Line Interface

The MHX-900 modem module is easily configured to meet a wide range of
needs and applications. You can have your modem perform a variety of
functions by sending it instructions (in the form of commands). Sending a
command overrides the modem’s operating characteristics.

Your modem must be in Command Mode for it to execute a command. If
you send characters when the modem is in Data Mode, the modem sends the
characters across the Wireless Link.

When the modem is initially powered up, the interface will operate in
command mode.

You can place the modem into Data Mode either by

1. Dialing a remote modem

2. Issuing the answer command

3. Issuing the online command
You can place the modem into Command Mode either by

1. Sending the escape sequence

2. Toggling the DTR line,

Refer to Appendix A (page

19) for a summary of the
modem commands

Configuration options are
not stored in non-volatile
memory until the WRITE
command (&W) is executed

Note: When the connection is lost to the remote modem, the modem will
switch to command mode.

To enter a command line and have your modem execute it, use the following
procedure:

1. With your modem in the Command Mode, type AT. These characters,
known as the attention characters, must be typed at the beginning or
each command line.

2. Type the command(s) in upper-case letters. Include any parameters
required by the command. To make the command line more readable,
you can insert as many spaces as desired. The command line holds up
to 40 characters, not including the AT prefix.

3. Press the ENTER key. Your modem executes the command line and
sends you a word response (usually OK).

For example, to set the Operating Mode S101 register to Master point to
point mode, enter the following command line; AT S101 = 1 <return>.

To display what a register is currently set to, enter the following command
line; AT Sxxx? <return>. The modem will output the value of the register.

MHX-900 Operating Manual: Chapter 3 Configuration Options 7