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.
Contents 1. Introduction 1.0 1.1 1.2 2. Initial Setup and Configuration 2.0 2.1 2.2 2.3 2.4 3. Product Overview ........................................................................................................................................................ 1 Features........................................................................................................................................................................ 1 About this Manual ...........................................
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.
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 m
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.
Top View Vcc Vcc Vcc Vcc Vcc Vcc Vcc Radio Radio Logic Logic Logic Logic Logic N/C /CONFIG /RESET GND GND GND GND GND GND GND N/C N/C N/C 1 40 20 21 N/C N/C N/C N/C N/C N/C N/C Rx Mode LED Tx Mode LED RSSI LED 3 RSSI LED 2 RSSI LED 1 CTS RTS DSR N/C DTR TxD RxD DCD Antenna Connector 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.
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.
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.
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.
Note: If you want to send more than one command line, wait for a response before entering the AT prefix at the start of the next command line. To re-execute the previous command, enter A/. The modem will execute the previous command line. For the AT command protocol, an escape sequence consists of three consecutive escape codes preceded and followed by at least 1 second of inactivity. Typically, the ‘+’character is used as the escape code. +++ preceded and followed by 1 second of inactivity 3.
Q Quiet Mode Your modem is preset to send responses when it executes commands, and there after to keep the host informed of its status. *Q0 Q1 V Enable modem responses Disable modem responses Result Codes display Your modem can either display result codes as words or numbers.
&S DSR (Data Set Ready) The &S command controls the DSR line for the modem, and determines when it is active &S0 *&S1 &V DSR is always ON DSR is ON in Data Mode, OFF in Command Mode View Configuration The &V command displays the current (DTE) baud rate, and all setable modem parameters including S register values. &W Write Configuration to memory The &W command stores the active configuration into the modem’s nonvolatile memory.
3.3 S Registers S Register 0 - Number of Rings - Auto Answer If this register is set to zero, the modem will power up in command mode. If this register is non-zero, the modem will power up in data mode. S Register 2 - Escape Code This register contains the ASCII value of the escape character. The default value (decimal 43) is equivalent to the ASCII character ‘+’. Values greater than 127 disable the escape feature and prevent you from returning to the Command Mode. Default is ‘+’(decimal 43).
S Register 101 - Operating Mode The Operating Mode (register S101) partly defines the “personality” of the MHX-900 module. Allowable settings for this register are 1 through 4. Default is 2 (Slave point to point). Each unit must be either a Master or Slave. Only one Master can exist for each network. Each unit should be configured as a Master or Slave.
S Register 102 - Serial Baud Rate The Serial Baud Rate is the current speed that the modem is using to communicate with the DTE. When the AT command prefix is issued, the modem performs an ‘autobaud’ operation and determines what the current DTE baud rate is set to. The S register value returns the current setting of the DTE baud rate.
S Register 104 - Network Address Select a Network Address and assign it to all units which will be included in the network. The Network Address defines the membership to which individual units can be a part of. By establishing a network under a common Network Address, the network can be isolated from any other concurrently operating network using the same hardware. As well, the Network Address provides a measure of privacy and security.
S Register 108 - Output Power Level The Output Power Level determines at what power the MHX-900 transmits. The super-sensitive MHX-900 can operate with very low power levels, so it is recommended that the lowest power necessary is used; using excessive power contributes to unnecessary “RF pollution”.
S Register 109 - Hopping Interval In a point-to-point network, the master and slave must be set to the same hopping interval. In a point-to-multipoint network, the hopping interval is controlled by the master. The slave units will use the hopping interval setting from the master. This option determines the frequency at which the modems change channel. Note that all modems must have the same hopping interval setting.
S Register 113 - Retry Limit This setting has a range of 0 to 255, and determines the number of attempts that will be made to retransmit data which failed the CRC checksum. Once the limit is reached, the modem will give up and discard the data. If the wireless connection is poor and data often needs to be retransmitted, a modem could be “tied up” trying to retransmit, thus holding up pending data.
S Register 113 - Retransmissions (Master Point to Multipoint) In a multipoint system, the Master does not receive acknowledgments from Slaves, and therefore has a slightly modified parameter called Retransmissions. The Master will retransmit each data packet exactly the number of times defined by the Retransmissions parameter. The Master retransmits once per hopping interval until the limit is reached.
A. Modem Command Summary The following provides a command summary for the MHX-900 module. Factory settings are denoted with a ‘*’.
20 MHX-900 Operating Manual: Appendix A Modem Command Summary
B. Serial Interface The MHX-900 module uses 8 pins on the 40 pin connector for asynchronous serial I/O. The interface conforms to TTL level RS-232 signals (ie. without level shifting), so direct connection to a host microprocessor is possible. The signals in the asynchronous serial interface are described below: DCD Data Carrier Detect - Output from Modem - When asserted (TTL low), DCD informs the DTE that a communications link has been established with another MHX-900.
22 MHX-900 Operating Manual: Appendix B Serial Interface
C. Sample Schematic Diagram The following is a sample microprocessor implementation with a MICROCHIP PIC 16C74 and the MHX-900. The MHX-900 performs no level shifting on the serial port, so direct connection to the host microprocessor is possible. DO NOT CONNECT THE MHX-900 TO RS 232 DRIVER OUTPUTS. DAMAGE TO THE UNIT MAY RESULT. On this implementation, the onboard SCI of the PIC 16C74 is directly connected pins 22 and 23 of the MHX-900.
24 MHX-900 Operating Manual: Appendix C Sample Schematic Diagram
D. Modem Setup Overview The required commands required to setup an MHX-900 module for point-to-point and point-to-multipoint 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.
26 MHX-900 Operating Manual: Appendix D Modem Setup Overview
E. Technical Specifications Electrical/Physical Data Interface Asynchronous Serial Port, TTL Levels RS-232 Signals Sig. Gnd, TX, RX, DCD, DSR, DTR, RTS, CTS Other Signals Reset, RxMode, TxMode, RSSI1, RSSI2, RSSI3 (All except Reset are status signals) AT Command line interface User Interface Bandwidth / Data Rate 2,400 - 115,200 bps, uncompressed half-duplex, Approx.
28 MHX-900 Operating Manual: Appendix E Technical Specifications
F. Glossary Terminology Used in the MHX-900 Operating Manual Asynchronous communications A method of telecommunications in which units of single bytes of data are sent separately and at an arbitrary time (not periodically or referenced to a clock). Bytes are “padded” with start and stop bits to distinguish each as a unit for the receiving end, which need not be synchronized with the sending terminal. Attenuation The loss of signal power through equipment, lines/cables, or other transmission devices.
can be controlled also by software using X-ON/XOFF (transmitter on/off) commands. Frequency-hopping A type of spread spectrum communication whereby the carrier frequency used between transmitter and receiver changes repeatedly in a synchronized fashion according to a specified algorithm or table. This minimizes unauthorized jamming (interference) and interception of telecommunications. Full-duplex Where data can be transmitted, simultaneously and independently, bidirectionally.
