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DNT500 

 2008 by RF Monolithics,

 

Inc. 

12 

M-0500-0000 Rev D 

does not create reserved time slots for remotes, extending the hop duration this way al-
lows several uncoordinated transmissions of user data and/or periodic/event reports to ar-
rive in the same slot with a relatively few collisions. 
 
The performance of a CSMA Mode 1 system can often be helped by setting the Min-
PacketLength and TxTimeout parameters on any remotes running transparent mode to 
non-zero values, especially if host messages only contain a few bytes each and transmis-
sion latency is not critical. For starting point values, set the MinPacketLength equal to the 
RemoteSlotSize and TxTimeout to at least three times the hop duration. This will help 
avoid excessive transmission collisions due to having many packets transmitted, each car-
rying only a small amount of user data on top of the relatively large packet overhead 
structure.  
 
For Example 2, consider a TDMA Mode 2 or 3 system operating at 500 kb/s. Up to 10 
registered remotes need to be accommodated. A BaseSlotSize of 138 bytes is needed, and 
each remote needs enough slot time to support a RemoteSlotSize of 64 bytes. The mini-
mum hop duration needed to support this configuration is: 
 

= 2.388 + 10*0.970 + 0.0160*(138 + 10*64) 
= 12.088 + 0.0160*778 
= 24.536 ms 

 
The closest programmable hop duration is 24.550 ms. 
 
In all TDMA modes, the base station operating system will commandeer one byte from 
the BaseSlotSize allocation for each registered remote to send ACKs to the remotes. The 
BaseSlotSize and MinPacketLength should be sized accordingly. 

2.7.4   Serial Port Operation 

DNT500 networks are often used for wireless communication of serial data. The 
DNT500 supports serial baud rates from 1.2 to 460.8 kb/s. Listed in the table below are 
the supported data rates and their related byte data rates and byte transmission times for 
an 8N1 serial port configuration: 
 

Baud Rate 

kb/s 

Byte Data Rate 

kB/s 

Byte Transmission Time 

ms 

1.2 0.12 

8.3333 

2.4 0.24 

4.1667 

4.8 0.48 

2.0833 

9.6 0.96 

1.0417 

19.2 1.92 

0.5208 

38.4 3.84 

0.2604 

115.2 11.52 0.0868 
230.4 23.04 0.0434 
460.8 46.08 0.0217 

 
To support continuous full-duplex serial port data flow, an RF data rate much higher than 
the serial port baud rate is required for FHSS. Radios transmissions are half duplex, and 

Summary of Contents for DNT500 Series

Page 1: ...DNT500 Series 900 MHz Spread Spectrum Wireless Industrial Transceivers Integration Guide 3079 Premiere Pkwy Ste 140 Norcross Georgia 30097 www rfm com 1 678 684 2000 ...

Page 2: ...Note This unit has been tested and found to comply with the limits for a Class B digital device pursuant to part 15 of the FCC Rules These limits are designed to provide reasonable protection against harmful interference when the equipment is operated in a commercial environment This equipment generates uses and can radiate radio frequency energy and if not installed and used in accordance with th...

Page 3: ...ion Planning 10 2 7 4 Serial Port Operation 12 2 7 5 Sleep Mode 13 3 DNT500 HARDWARE 14 3 1 Specifications 15 3 2 Module Interface 16 3 3 Input Voltages 17 3 4 ESD and Transient Protection 17 3 5 Interfacing to 5 V Logic Systems 18 3 6 Power On Reset Requirements 18 3 7 Analog RSSI Output 18 3 8 Mounting and Enclosures 18 3 9 Connecting Antennas 19 3 10 Labeling and Notices 19 4 PROTOCOL MESSAGES ...

Page 4: ...mples 37 5 DNT500 DEVELOPER S KIT 38 5 1 DNT500DK Kit Contents 38 5 2 Additional Items Needed 38 5 3 Developer s Kit Default Operating Configuration 39 5 4 Development Kit Hardware Assembly 39 5 5 DNT500 Wizard Utility Program 41 5 6 DNT500 Interface Board Features 47 6 Demonstration Procedure 50 7 Troubleshooting 51 8 APPENDICES 52 8 1 Ordering Information 52 8 2 Technical Support 52 8 3 DNT500 M...

Page 5: ...n when powered off Dynamic TDMA slot assignment that maximizes throughput Simple serial interface handles both data and control at up to 460 8 kb s 1 1 Why Spread Spectrum A radio transmission channel can be very hostile corrupted by noise path loss and interfering transmissions from other radios Even in an interference free environment radio performance faces serious degradation through a phenome...

Page 6: ...e spread spectrum is produced by multiplying the transmitted data stream by a much faster noise like repeating pat tern The ratio by which this modulating pattern exceeds the bit rate of the base band data is called the processing gain and is equal to the amount of rejection the system affords against narrowband interference from multipath and jammers Transmitting the data signal as usual but vary...

Page 7: ... these channels are the same from trip to trip they can be memorized and avoided Unfortunately this is generally not the case as it may take several seconds to completely cover the hop sequence during which time the multipath delay profile may have changed substantially To ensure seamless operation throughout these outages a hopping radio must be capable of buffering its data until a clear channel...

Page 8: ...etwork Registration can be handled automatically by the base station or it can be controlled by allowing the base station host application to authenti cate the remote for registration When a remote is registered it receives several network parameters from the base station including HopDuration Nwk_ID FrequencyBand and Nwk_Key see Section 5 2 for parameter details Note that if a registration parame...

Page 9: ...of each hop the base station transmits a synchronizing signal After the synchronizing signal has been sent the base will transmit any user data in its transmit buffer unless in transparent mode the MinPacketLength and or TxTimeout parameters have been set to non zero The maximum amount of user data that the base station can transmit per hop is limited by the BaseSlotSize parameter which has a maxi...

Page 10: ... Network Operation Most point to point networks act as serial cable replacements and both the base station and the remote use transparent mode Unless the MinPacketLength and TxTimeout pa rameters have been set to non zero the base station will send the data in its transmit buffer on each hop up to the limit set by the BaseSlotSize parameter less ACK bytes If the base station is buffering more data...

Page 11: ...ex Serial Data Communications From an host application s perspective DNT500 serial communications appear full du plex Both the base station host application and each remote host application can send and receive serial data at the same time At the radio level the base station and remotes do not actually transmit at the same time If they did the transmissions would collide As discussed earlier the b...

Page 12: ...acking is not required The illustration below com pares TDMA to CSMA operation There are two important parameters related to CSMA operation The CSMA_MaxBackoff parameter defines the maximum time that a remote will wait after a collision before at tempting to send the packet again back off interval The CSMA_Persistence parameter sets the probability that a remote will transmit immediately rather th...

Page 13: ... CONNECT message for its host when a remote registers and a DISCONNECT mes sage when the remote s registration lease expires The base station in a CSMA network can generate CONNECT messages for more than 255 remotes This allows the host application to track remotes entering and leaving a large CSMA network by creating a table of MAC addresses and periodically sending a ping to each remote in the t...

Page 14: ... in the shared slot The user s application must ensure that no more than one PTT re mote is using the slot at a time 2 7 3 Network Configuration Planning Some planning is necessary for a DNT500 network to coordinate the RF_DataRate HopDuration BaseSlotSize RemoteSlotSize MinPacketLength TxTimeout and TDMA_MaxNumSlots parameters to achieve a practical configuration This is true even for modes that ...

Page 15: ...ter in bytes The constants in the equation for each RF data rate are given in the following table RF Data Rate kb s TBRO ms TRO ms TRFB ms 38 40 11 620 4 817 0 2080 115 2 4 953 2 039 0 0694 200 3 540 1 450 0 0400 500 2 388 0 970 0 0160 For Example 1 consider a point to point CSMA Mode 0 system operating at 38 4 kb s with the BaseSlotSize parameter set to 133 bytes and the RemoteSlotSize parameter ...

Page 16: ...SlotSize of 138 bytes is needed and each remote needs enough slot time to support a RemoteSlotSize of 64 bytes The mini mum hop duration needed to support this configuration is 2 388 10 0 970 0 0160 138 10 64 12 088 0 0160 778 24 536 ms The closest programmable hop duration is 24 550 ms In all TDMA modes the base station operating system will commandeer one byte from the BaseSlotSize allocation fo...

Page 17: ...d heavy industrial process environments Most applications do not require continuous serial port data flow The DNT500 transmit and receive buffers hold at least 1024 bytes and will accept brief bursts of data at high baud rates provided the average serial port data flow such as shown in Example 3 is not exceeded It is strongly recommended that the DNT500 host use hardware flow control The host must...

Page 18: ...terns compatible the frequency alloca tions in the US Canadian Australian and New Zealand The DNT500 has six selectable RF output power levels 0 10 19 24 27 and 28 dBm Also there are four selectable RF transmission rates 38 4 115 2 200 and 500 kb s The power level is firmware inter locked to a maximum of 19 dBm at 500 kb s to assure regulatory compliance The DNT500 includes a low noise preamplifie...

Page 19: ...h Access Schemes TDMA and CSMA Number of Network Nodes TDMA 15 CSMA 1024 ADC Input Range 0 3 3 V ADC Input Resolution 10 bits Signal Source Impedance for ADC Reading 10 KΩ PWM DAC Output Range 0 3 3 V PWM DAC Output Resolution 8 bits Primary Serial Port Baud Rates 1 2 2 4 4 8 9 6 19 2 38 4 115 2 230 4 460 8 kb s Diagnostic Serial Port Baud Rates 38 4 115 2 230 4 460 8 kb s Digital I O Logic Low In...

Page 20: ...n switched low after sleep the module executes a power on reset 12 ADC0 10 bit ADC input 0 Full scale reading is referenced to the ADC_REF input 13 ADC1 10 bit ADC input 1 Full scale reading is referenced to the ADC_REF input 14 ADC2 10 bit ADC input 2 Full scale reading is referenced to the ADC_REF input 15 EX_SYNC Optional rising edge triggered input for synchronizing co located base stations Se...

Page 21: ...nly Connect to the host circuit board ground plane 42 RFIO Alternate RF port to the U FL connector DNT500 only The antenna can be connected to this port with a 50 Ω stripline or coaxial cable Leave unconnected when using the U FL connector 43 GND RF ground DNT500 only Connect to the host circuit board ground plane 3 3 Input Voltages DNT500 radio modules can operated from an unregulated DC input Pa...

Page 22: ...gnored 3 7 Analog RSSI Output Pin 4 on the DNT500 provides a 0 3 to 3 0 V output proportional to received signal strength in dB as follows VRSSI 0 03 SRF 3 6 Where VRSSI is the RSSI output in volts over the range of 0 3 to 3 0 V SRF is the RF signal strength in dBm over the range of 110 to 20 dBm The analog RSSI output on a DNT500 remote represents the signal strength of the last base station tran...

Page 23: ...onjunction with any other antenna or transmitter DNT500 FCC Notices and Labels This device complies with Part 15 of the FCC rules Operation is subject to the following two conditions 1 this device may not cause harm ful interference and 2 this device must accept any interference received including in terference that may cause undesired operation A clearly visible label is required on the outside o...

Page 24: ...is a modifier indicat ing that the message is a command or a reply A reply message has the original com mand type in bits 3 0 with bit 4 set to one Arguments vary in size and number depending on the type of message and whether it is a message sent from the host or is a reply from the radio see the table provided be low for reference The LRC is an optional checksum byte that verifies the integrity ...

Page 25: ...ne 0x11 ExitProtocolModeReply from Radio none 0x02 SoftwareReset from Host BootSelect 0x12 SoftwareResetReply from Radio none 0x03 GetRegister from Host Reg Bank Span 0x13 GetRegisterReply from Radio Reg Bank Span Val 0x04 SetRegister from Host Reg Bank Span Val 0x14 SetRegisterReply from Radio none 0x05 TxData from Host Addr Data 0x15 TxDataReply from Radio TxStatus Addr RSSI 0x26 RxData from Rad...

Page 26: ...A remote has joined me MacAddr 0xFF if none A3 Remote Joined a network ready for data NwkID BaseMacAddr Range A4 Remote Exited network base is out of range NwkID A5 Remote Base has restarted none A7 Base Remote has left the network Addr Status codes for error conditions Add l fields E0 Protocol error invalid message type none E1 Protocol error invalid argument none E2 Protocol error general error ...

Page 27: ...0x6C 0x64 There are 15 bytes following the length byte so the length byte is set to 0x0F Note that the 0x000102 MAC address is entered in Little Endian byte order 0x02 0x01 0x00 When an ACK to this message is received from the remote the base station outputs a TxDataReply message to its host 0xFB 0x06 0x15 0x00 0x02 0x01 0x00 0x80 The 0x00 TxStatus byte value indicates the ACK reception from the r...

Page 28: ... radio remote base or PTT remote listen mostly re mote Note that the setting takes effect immediately RF_DataRate This sets the over the air RF data rate Radios with different RF rates cannot intercom municate The following codes are defined 0x00 500 kb s 0x01 200 kb s 0x02 115 2 kb s 0x03 38 4 kb s 0xff auto default A setting of auto will cause a remote to scan all 4 possible RF rates for a netwo...

Page 29: ...er of superframes that a remote will sleep between wake intervals A superframe interval is 64 hops TxPower Sets the transmit power level 0 0 dBm or 1 mW 1 10 dBm or 10 mW default 2 19 dBm or 79 4 mW 3 24 dBm or 250 mW 4 27 dBm or 500 mW 5 28 dBm or 1000 mW 1 W When the data rate is set to 500 kb s the firmware interlocks the transmit power level to 19 dBm or less to comply with FCC regulations Ext...

Page 30: ... 255 5 ms 01 09 MaxPropDelay R W 1 0 255 50 µs 4 miles 01 0A EpochMode R W 1 0 1 0 use previous 1 increment 2 random Note The base station propagates these setting to all remotes FrequencyBand This sets the range of frequencies over which the radio will operate Two settings are de fined North America 902 928 MHz and Australia New Zealand 915 928 MHz AccessMode This sets the channel access mode tha...

Page 31: ...Q_AttemptLimit This sets the maximum number of attempts that will be made to send a data packet on the RF link Setting this parameter to the maximum value of 15 is a flag value indicating that there should be no limit to the number of attempts to send each packet infinite number of attempts This mode is intended for point to point networks in serial data cable replace ment applications where absol...

Page 32: ...TDMA_CurrSlot R 1 0 15 current slot 02 0C HardwareVersion R 1 0 255 0x00 DNT500 rev A 02 0D FirmwareVersion R 1 0 255 current firmware load 02 0E FirmwareBuildNum R 2 0 216 current firmware load 02 0F Epoch R 1 0 255 as set 02 10 SuperframeCount R 1 0 255 current value 02 11 RSSI_Idle R 1 0 255 as set 02 12 RSSI_Last R 1 0 255 as set 02 14 CurrAttemptLimit R 1 0 255 as set 02 15 CurrRangeDelay R 1...

Page 33: ...is value is read only In manual TDMA mode and CSMA mode this value must be set by the user This value excludes the message length byte REMT_STATUS packet and checksum and CRC bytes It indicates the number of bytes available for REMT_DATA and or REMT_DATA_EXTs It does not include the overhead bytes required for these packets which must be figured into the slot size budget TDMA_NumSlots In TDMA acce...

Page 34: ...it This returns the value of ARQ_AttemptLimit currently in use depending on the selected ARQ_Mode it may not always match the local EEPROM value CurrRangeDelay This returns the current propagation delay for this remote as measured from the base 4 2 4 Bank 3 Serial Size in Bank Loc n Name R W bytes Range Default 03 00 SerialRate R W 2 0 216 115 2 kb s 0x0004 03 01 SerialParams R W 1 0 7 8N1 03 03 S...

Page 35: ... control lines Ena bling or disabling response to some serial control signals can facilitate communicating with devices that support only a reduced serial interface The register is defined as a bit mask with the following options bits 7 3 Reserved bit 2 Base DCD mode 1 The base will only assert DCD when at least one remote is registered default 0 The base always asserts DCD regardless of whether a...

Page 36: ...ion on the serial host protocol for more information ProtocolOptions This is a bitmask that selects various options for the protocol mode Default is 0x01 bit 7 Enable output of Instrumentation packets bits 2 6 reserved bit 1 Enable LRC checksum byte in serial protocol bit 0 Enable output of Announce packets TxTimeout This sets the transmit timeout used for determining message boundaries in transpa...

Page 37: ...ns that are enabled as inputs enables or disables the internal pull up Reading these registers returns the current level detected on the corresponding pin ADC0 2 Read only returns the current 10 bit ADC reading for the selected register See the dis cussion of the ADC_SampleIntvl parameter below PWM0 1 Sets the PWM DAC outputs The DC voltage derived from the integrated low pass fil ters on the PWM ...

Page 38: ...d as inputs this sets the initial pull up setting PWM0_Init This sets the initial value for PWM0 at startup PWM1_Init This sets the initial value for PWM1 at startup GPIO_Alt Provides and alternate function for GPIO3 as an RS 485 driver enable GPIO_MessageMode This register enables a message to be sent to the base station whenever one of the GPIOs is triggered If the radio is asleep it will be awa...

Page 39: ...spond to GPIO0 GPIO2 ADC_SampleIntvl The ADC_SampleIntvl sets the interval between the beginning of one ADC read cycle and the next ADC read cycle The three ADC inputs are read on each ADC read cycle An ADC_SampleIntvl count equals 10 ms ADC0 2_ThresholdLo Hi These values define thresholds to trigger an I O report based on ADC measurements If I O reporting is enabled single EVENT report containing...

Page 40: ...ings to EEPROM When programming registers all changes are considered temporary until this command is executed 4 2 9 Protocol Mode Configuration Sensor Message Examples For Example 5 the host configures the base station to transmit 24 dBm of RF power us ing the SetRegister command 0x04 The TxPower parameter is stored in bank 0x00 reg ister 0x18 A one byte parameter value of 0x03 selects the 24 dBm ...

Page 41: ...IO_MessageMode with a SetRemoteRegister command GPIO_MessageMode is register 0x03 of bank 0x06 Bits 4 5 control GPIO2 event messaging Button Message mode is chosen which sends the state of GPIO2 located in register 0x02 of bank 0x05 when a high to low transition oc curs on GPIO2 Button Message always reports a low state The required GPIO_Mes sageMode bit pattern is 00010000b or 0x10 The protocol f...

Page 42: ...wer Suppliers 120 240 VAC Two U FL RF Jumper Cables Two RJ 45 to DB 9F Cable Assemblies Two A B USB Cables One RJ 11 to DB 9F Cable Assembly Two 900 MHz Dipole Antennas One DNT500 Documentation and Software CD 5 2 Additional Items Needed To operate the kit the following additional items are needed Two PCs with Microsoft Windows XP or Vista Operating System To fully test the kit s functionality the...

Page 43: ...ting will overload the DNT500P receiver and cause erratic operation 5 4 Development Kit Hardware Assembly Observe ESD precautions when handling the kit circuit boards Referring to Figure 5 4 1 confirm each DNT500P is correctly plugged into an interface board with the radio ori ented so that its U FL connector is next to the U FL connector on the interface board Check each radio s alignment in the ...

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