Operating Manual MHX-920 900 MHz Spread Spectrum OEM Transceiver Revision 1.20, December 21, 2000 Microhard Systems Inc. #110, 1144 - 29th Ave. N.E. Calgary, Alberta T2E 7P1 Phone: (403) 248-0028 Fax: (403) 248-2762 www.microhardcorp.
MHX-920 900 MHz Spread-Spectrum Embedded Modem WARNING In order to comply with the FCC/IC adopted RF exposure requirements, this transmitter system will be installed by the manufacturer's reseller professional. Installation of all antennas must be performed in a manner that will provide at least 23 cm clearance from the front radiating aperture, to any user or member of the public. This manual contains information of proprietary interest to Microhard Systems Inc.
Contents 1. 2. 3. 4. iii Introduction 1.0 Product Overview .............................................................................................................................................................................. 1 1.1 Features.............................................................................................................................................................................................. 1 1.2 About this Manual ............................................
A. B. C. D. E F. G. H. I. S Register 120 - RTS/DCD Framing................................................................................................................................................. 33 S Register 121 - DCD Timeout......................................................................................................................................................... 33 S Register 122 - Remote Control .......................................................................................
1. Introduction 1.0 Product Overview The MHX-920 is a high-performance embedded wireless data transceiver. Operating in the 902 - 928 MHz ISM band, this frequency-hopping spreadspectrum module is capable of providing reliable wireless data transfer between almost any type of equipment which uses an asynchronous serial interface. The small-size and superior RF performance of this module make it ideal for many applications.
n 64 sets of user-selectable pseudo-random hopping patterns, intelligently designed 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-920 module uses a subset of standard A
2. Electrical/Physical 2.0 Functional Block Diagram DVcc AVcc Mixer LNA Antenna Switch IF Demod GND - + Frequency Synthesizer Comparator Mixer PA GAIN RSSI1-3 \Config \Reset RXMODE TXMODE uC A/D SRAM EEPROM 8 bit data bus TxD RTS DTR UART (DCE) RxD CTS DSR DCD Figure 1.
2.1 Pinout Figure 2 provides a top-view pinout drawing of the MHX-920 module. The corner pins (1,20,21,40) are labeled directly on the module. AVcc AVcc DVcc DVcc DVcc DVcc DVcc NC \Config \Reset GND GND GND GND GND GND GND NC NC NC 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 MHX-910 40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21 NC NC NC NC NC NC NC Rx/SYNC TxMODE RSSI3 RSSI2 RSSI1 CTS RTS DSR NC DTR TxD RxD DCD Figure 2 - Pinout (Top View) Table 1.
Table 1 (continued) GND 11-17 Ground reference for logic, radio and I/O pins. \Reset 10 Active low reset input to the module. See Section 2.4 for timing information. I RSSI1 29 Receive Signal Strength Indicator 1. This output is the first of the three RSSI indicators to become active high as the signal strength increases. See Section 2.2 for details O RSSI2 30 Receive Signal Strength Indicator 2. This output is the second RSSI indicator to become active high as the signal strength increases.
2.2 LED OPERATION LED functionality is dependent on the mode of operation. Lines RX/SYNC, TXMODE, and RSSI1,2 and 3 are designed to drive LED’s (active high). Table 2 explains LED operation for the various modes. Table 2.
Signal strength, which is also reported in Register S123, is calculated based on the last four valid received packets with correct CRC, and represented by RSSI1, 2 and 3. For slaves, packets are received on every single hop either from a repeater, or the master. When calculating RSSI, the master takes into consideration all packets received from slaves and repeaters. Repeaters and slaves only transmit back to the master when they have information to send.
2.3 DC Characteristics Sym Characteristic Min Typ Max Units AVCC Radio Supply Voltage 4.9 5.0 5.5 V DVCC Logic Supply Voltage 4.75 5.0 5.5 V VPOT Power On Reset Threshold Voltage 1.8 2 2.
2.4 AC Characteristics Sym Characteristic Min TTOUT Reset Delay Time-Out Period TR2D Internal Reset to Data Mode* TR2C Internal Reset to Command Mode Typ Max 500 0 ms 5 0 Units s ms *Unit will enter into Command Mode upon power up if register S0=0. Unit will enter into Data Mode upon power-up if register S0=1. When powering up into Data Mode, an additional delay of 5 seconds is added if Register S119=1. See page 14 for details.
10 MHX-920 Operating Manual: Chapter 3 Modes of Operation
3. Modes of Operation The MHX-920 modem can be easily configured to meet a wide range of needs and applications. The module is designed such that all communication is through one serial port (Pins 21 to 28 on the module). This port has two functions: 1. It provides the asynchronous interface with the host equipment for data that is sent/received on the RF channel. When operating in this fashion, the module is said to be in data mode. 2. It is also used for configuring and programming the module.
n Master Point-to-Point: The modem is configured to communicate with a single Slave, either directly, or through one or more Repeaters. n Master Point-to-Multipoint: The modem is configured to communicate with one or more Slaves and/or Repeaters. n Slave: The modem is configured to communicate with one Master either directly or through one or more Repeaters..
3.2.
DATA MODE (ATA or A TO Com man d) Esc DT ape R o Seq r uen ce 5 sec elapses or characters other than 'mhx' entered by the user COMMAND MODE USER TYPES 'mhx' POWER-UP SEQUENCE Figure 5A. S0=1, S119=1 (factory default) (AT Ao rA TO Com man d) Es DT cap R e S or equ enc e Issuing the answer command (ATA ); or, • Issuing the online command (ATO ). To return to Command Mode, you can either: Figure 5B. S0=1, S119=0 • Send the escape sequence.
4. Configuration This chapter provides a detailed description of the various operating parameters of the MHX-920. Section 4.1 provides a quick-start approach which outlines the minimum requirements for establishing communication between two MHX-920 modules. The settings will not necessarily provide optimal performance for your application, but will verify that the modules are functioning correctly. Section 4.2 describes the AT Command interface, and the various AT Commands. Section 4.
The units should now be communicating. Remember, the parameters defined by Factory Settings 1 and 2 will likely not be the most ideal for your application, but will quickly allow you to test the units. A complete summary of the settings defined by all four factory settings can be found in Appendix C. Factory Default Settings. Settings are not immediately stored in non-volatile memory, therefore, the command &W is issued to store the current configuration into non-volatile memory.
Note that the terminal must be configured to the same baud rate as the modem in order for the modem to recognize the escape sequence. The modem is unable to “autobaud” while in Data Mode. The following is a description of all available commands. ‘*’ denotes standard factory settings. All of the following commands must be preceded by “AT”. A Answer The A command puts the modem into data mode, where the modem attempts to communicate with other compatibly configured modems (Type ATA ).
W Connection Result This parameter determines the modem response at the transition from Data Mode to Command Mode *W0 W1 W2 Z Refer to Appendix A (page 19) for a summary of the modem commands Reports computer (DTE) baud rate as CONNECT xxxx Reports wireless rate between modems as CARRIER xxxx. Reports modem (DCE) baud rate as CONNECT xxxx Reset and load stored configuration The Z command resets the modem and loads the stored configuration.
&S DSR (Data Set Ready) The &S command controls the DSR line for the modem, and determines when it is active &S0 DSR is always ON *&S1 DSR is ON in Data Mode, OFF in Command Mode &S2 DTR/DSR signaling. With &S2, Slaves and repeaters output the state of the master’s DTR on their local DSR line. Master outputs the state of a slave’s DTR on its local DSR line only in point-to-point mode (i.e., DTR is a two-way signal transfer in pointto-point mode, and a one-way signal transfer in point-to-multipoint mode).
AT Command Result Codes The MHX-920 module can display the results of a command as either text strings or numerical data. The following chart shows resulting text string and corresponding numeric result.
4.3 S Registers Refer to Appendix A (page 45) for a summary of the S-Registers. The S Registers described in this section affect the operating characteristics of the modem. S Register 0 - Auto Answer If this register is set to zero, the modem will power up in command mode. If this register is set to one, the modem will power up in data mode. S Registers 2 through 5 cannot be stored to nonvolatile memory. S Register 2 - Escape Code This register contains the ASCII value of the escape character.
S Register 101 - Operating Mode Only one Master can exist for each network. The Operating Mode (register S101) partly defines the “personality” of the MHX-920 module. Allowable settings for this register are 1 through 5 as follows:. • • • • • S101=1 S101=2 S101=3 S101=4 S101=5 Master Point to Multipoint Master Point to Point Slave Repeater Master - Diagnostics (see Section 4.
3)Slave. Up to 65535 Slaves may exist in a network, all of which communicate with the common Master (either directly or via Repeater(s)). Slaves cannot directly communicate with other. Slaves only provide acknowledgement for packets of data sent by the Master when the Master is in Point-to-Point mode. In multipoint mode, multiple slaves would conflict with one another if they were all trying to acknowledge the Master at the same time.
S Register 102 - Serial Baud Rate The Serial Baud Rate is the current speed that the modem is using to communicate with the DTE. In command mode, the module “autobauds,” meaning that it will adapt to the baud rate of the DTE equipment to which it is connected. Therefore, when in command mode, you may change the baud rate of your equipment, and the MHX-920 will automatically adjust to this baud rate once an AT string is issued. The new baud rate is stored in register S102.
S Register 104 - Network Address Select a Network Address and assign it to all units which will be included in the network. Warning: Microhard Systems strongly recommends changing the Network Address to a value different than the factory default before deploying 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.
the following diagrams illustrate the methodology for deploying simple to complicated networks: Master Slave Master Repeater Master Repeater1 M[1] ←→ S1[1] M[1] ←→ R1[1,2] ←→ S2[2] M[1] ←→ R1[1,2] ←→ R2[2,3] ←→ S3[3] M[1] ←→ R1[1,2] ←→ R2[2,3] ←→ R3[3,4] ←→ S4[4] Slave Repeater2 Slave It is reasonable to consider a Repeater as being both a Slave and a Master, alternating between Primary and Secondary Hopping Patterns as the unit changes channel.
S Register 107 - Encryption Key All units within a network must use the same encryption key. The Encryption Key provides a measure of security and privacy of communications by rendering the transmitted data useless without the correct key on the receiver. Valid Encryption Keys range from 0 to 65535. Warning: Microhard Systems strongly recommends changing the Encryption Key to a value different than the factory default before deploying the network.
IMPORTANT: FCC Regulations allow up to 36 dBi effective radiated power (ERP). Therefore, the sum of the transmitted power (in dBm), the cabling loss and the antenna gain cannot exceed 36 dBi. 1 mW = 0 dBm 10 mW = 10 dBm 100 mW = 20 dBm 1000 mW = 30 dBm For example, when transmitting 1 Watt (30 dBm), the antenna gain cannot exceed 36 - 30 = 6 dBi. If an antenna with a gain higher than 6 dBi were to be used, the power setting must be adjusted appropriately. Microhard Systems Inc.
S Register 110 - Data Format This register determines the format of the data on the serial port.
S Register 114 - Packet Size Control This register, when set to 1, allows for Repeater and Slaves’ local S111 and S112 to override those of the Master when the system is operating in pointto-point mode. This may be useful for controlled asymmetrical data flow. The master always transmits in the first portion of the hop interval, with slaves and repeaters responding back to the master on the second portion of the hop interval.
S Register 213 - Packet Retry Limit Packet Retry Limit is analogous to Packet Retransmissions, but specifically applies to Slaves and Repeaters. This parameter is not used by the Master. Because the Slave has the advantage of receiving acknowledgements from the Master, it is not necessary to blindly retransmit each packet. If the Slave does not get an acknowledgement on the next hop, it will retransmit its packet. This will continue until the Packet Retry Limit is reached or an acknowledgement is received.
S Register 117 - Modbus Mode Modbus Mode allows for the MHX-920 to be fully Modbus compatible. For Modbus operation, the general requirement is to get the packet of data to the receiving serial port with no gaps in the data. The MHX-920 incorporates a “Modbus Mode” which implements a delay at the receiving modem to ensure that no gaps are introduced. For most applications, the following settings are suitable for Modbus operation: 1. Set Modbus Mode parameter S117 = 1 2.
S Register 118 - Roaming This mode is activated on slaves and repeaters by setting register S118=1. In this mode, a slave/repeater looks for synchronization with a Master having the same network address and encryption key, but without regard for the hopping pattern S106. Once the slave/repeater finds such a master, it tunes to that master’s hopping pattern. If synchronization is lost, the slave/repeater will again begin searching for a new master.
To enable output (DCD) data framing, set the Data Carrier Detect parameter as &C2. This type of framing uses both S120 and S121 registers as shown in Figure 10. Valid ranges for each parameter are 0 to 254 ms DCD RXD Data leaving MHX-910 S120 (ms) S121 (ms) Figure 10 - Output Data Framing S Register 122 - Remote Control This register either disables or enables remote control at a repeater or slave unit.
4.4 Diagnostics, Statistics and Remote Control The MHX-920 provides several commands which are very useful for troubleshooting and analyzing the performance of the radio system. 4.4.1 Spectrum Analyzer Feature (ATG) Issuing the command ATG ,causes the MHX-920 to perform a sweep of the entire operating spectrum, giving a signal strength read-out in dBm for each channel as shown below: Noise level, '*'- mean value, '.
4.4.3 Remote Control and Diagnostics (S101=5) This is a very powerful tool which allows user to remotely configure and interrogate all units in a multipoint system from the Master unit. Simply by having knowledge of the unit address of each slave/repeater in the system, users can set the unit address of the master to match that of the slave/repeater of interest, set S101=5, go online, and interrogate/modify virtually all parameters of the remote repeater/slave unit.
Table 4 - Remote Control and Diagnostics Command Remote Register Description 0(x) S101 Operating Mode 1(x) S102 Baud Rate 2(x) S108 Output Power 3(x) S110 Data Format 4(x) S115 Repeat Interval 5(x) S116 Character Timeout 6(x) S120 RTS/DCD Framing 7(x) S121 DCD Timeout 8(x) S117 Modbus Mode 9(x) S213 Retry Limit a test string Read back 'OK' from remote a1 test string a2 test string a3 test string b(x) &E Read back 'Microhard Systems, Inc.
As mentioned previously in this section, there are some settings that can be changed to the master’s own registers while in diagnostics mode. The most useful is the unit address. By changing the master’s unit address to that of another slave in the network while in diagnostics mode, users can quickly interrogate/modify many different slave’s settings without the delays associated with switching between command and data modes. The commands which apply to the master’s own registers are shown in Table 5.
5. Installation The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personnel. The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personel. The MHX-920 complies with FCC part 15 at the modular level for operation in the license-free 902-928 MHz ISM band. This chapter provides guidelines for installing and deploying equipment which incorporates the MHX-920 module. 5.
Base Height (m) Mobile Height (m) Distance (km) When deploying your system, care must be taken to ensure the path loss (reduction of signal strength from transmitter to receiver in dB) between equipment does not exceed the system gain (140 dB in the above example). It is recommended to design for a gain margin of at least 10 dB to ensure reliable communication. Gain margin is the difference between system gain and path loss.
5.2 Antennas and Cabling This section describes the recommended procedure for installing cabling and antennas for use with the MHX-920 module. 5.2.1 Internal Cabling The most common method for installing the module is to run a cable from the module’s MCX connector to a reverse TNC bulkhead connector on the chassis of the equipment as shown in Figure 11. This cable can be purchased from Microhard Systems.
5.2.2 Installing External Cables, Antennas and Lightning Arrestors The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personnel. The installation, removal or maintenance of all antenna components must be carried out by qualified and experienced personnel. Never work on an antenna system when there is lightning in the area. Direct human contact with the antenna is potentially unhealthy when the MHX-920 is generating RF energy.
Antenna Before choosing an antenna, you should have some knowledge of the path loss and the topology of the equipment. If the equipment is in a fixed location and is to communicate with only one other unit also in a fixed location, then a Yagi antenna is suitable. Choose a Yagi with enough gain to ensure adequate gain margin. When deploying the Yagi, point the antenna towards the intended target, ensuring the antenna elements are perpendicular to the ground.
44 MHX-920 Operating Manual: Chapter 5 Installation
A. Modem Command Summary The following provides a command summary for the MHX-920 module. Factory settings are denoted with a ‘*’.
46 MHX-920 Operating Manual: Appendix A Modem Command Summary
B. Serial Interface The MHX-920 module uses 8 pins on the header connector for asynchronous serial I/O. The interface conforms to standard RS-232 signals 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-920.
48 MHX-920 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-920. The MHX-920 performs no level shifting on the serial port, so direct connection to the host microprocessor is possible. DO NOT CONNECT THE MHX-920 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 2 and 3 of the MHX-920.
50 MHX-920 Operating Manual: Appendix C Sample Schematic Diagram
D.
52 MHX-920 Operating Manual: Appendix D Factory Default Settings
E. Performance Tables The scope of this appendix is to find the best possible performance and maximum packet size at different modes of operation. The setup assumes a baud rate of 115k, no retries and no retransmissions. WARNING: Communication will fail if the maximum packet size (S112) exceeds the recommended optimal packet size. . Slave <--> Master Communication. (No Repeater) Link Rate S103=2 Slave <--> Master Communication. (No Repeater) Link Rate S103=4 Repeater <--> Master Direct Communication.
54 MHX-920 Operating Manual: Appendix E.
F. Hopping Patterns This Appendix provides a guide for selecting appropriate hopping patterns (S106,S206). There are 64 hopping patterns: The first 62 come pre-programmed from the factory as per the table below. There are 31 patterns in Group A and 31 in Group B. When deploying a network, it is recommended that you use choose hopping patterns all belonging to the same group. Patterns have been designed to notch out certain segments of the ISM band. Pattern Number Spectrum Used 0, 2, 4, 6, 8, 10, 12 902.
56 MHX-920 Operating Manual: Appendix F.
G. Technical Specifications Electrical/Physical Data Interface Asynchronous Serial Port, TTL Levels Signals Sig. Gnd, TX, RX, DCD, DSR, DTR, RTS, CTS Bandwidth / Data Rate 2,400 - 115,200 bps, uncompressed half-duplex, Approx. 85 kbps sustained in intelligent asymmetrical full-duplex transmission mode Communications Range1 30 kilometres (19 miles) Power Requirements 5 VDC, 1.
58 MHX-920 Operating Manual: Appendix H.
MHX-920 Operating Manual: Appendix H. Mechanical Drawing 750 21 20 3500 Dimensions in thousandths of an inch. Shaded areas = keep clear. 600 2100 125 40 Pin 1 100 Top View 200 275 1900 Document Number: D1042-02 Friday, July 14, 2000 Size A 800 Rev. 2 Sheet 1 of 1 #110, 1144 - 29th Ave. N.E. Calgary, Alberta, Canada T2E 7P1 Drawn By: NB MHX Series Mechanical Drawing Microhard Systems Inc. 225 170 450 dia. 90 H.
60 MHX-920 Operating Manual: Appendix H.
I. Glossary Terminology Used in the MHX-920 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.
