RFM DNT900 Series Quick setup guide

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DNT900 Series
900 MHz Spread Spectrum
Wireless Transceivers
Integration Guide

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Important Regulatory Information
RFM Product FCC ID: HSW-DNT900P
IC 4492A-DNT900P
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 the in-
struction manual, may cause harmful interference to radio communications. Operation of this equipment
in a residential area is likely to cause harmful interference in which case the user will be required to
correct the interference at their expense.
FCC Antenna Gain Restriction:
The DNT900 has been designed to operate with any dipole antenna of up to 5.1 dBi of gain, or any Yagi
of up to 6.1 dBi gain.
The antenna(s) used for this transmitter must be installed to provide a separation distance of at least
20 cm from all persons and must not be co-located or operating in conjunction with any other antenna or
transmitter.
IC RSS-210 Detachable Antenna Gain Restriction:
This device has been designed to operate with the antennas listed below, and having a maximum gain of
6.1 dB. Antennas not included in this list or having a gain greater than 6.1 dB are strictly prohibited for
use with this device. The required antenna impedance is 50 ohms:
RFM RWA092R Omnidirectional Dipole Antenna, 2 dBi
RFM OMNI095 Omnidirectional Dipole Antenna, 5 dBi
RFM YAGI099 Directional Antenna, 6.1 dBi
To reduce potential radio interference to other users, the antenna type and its gain should be so chosen
that the equivalent isotropically radiated power (e.i.r.p.) is not more than that permitted for successful
communication.
See Section 3.9 of this manual for regulatory notices and labeling requirements. Changes or modifica-
tions to a DNT900 not expressly approved by RFM may void the user’s authority to operate the module.

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Table of Contents
1.0 Introduction ...................................................................................................................................... 5
1.1 Why Spread Spectrum? ............................................................................................................... 5
1.2 Frequency Hopping versus Direct Sequence............................................................................... 6
2.0 DNT900 Radio Operation................................................................................................................ 7
2.1 Network Synchronization and Registration .................................................................................. 7
2.2 Authentication............................................................................................................................... 8
2.3 Serial Port Modes......................................................................................................................... 9
2.4 SPI Port Modes ............................................................................................................................ 9
2.5 RF Data Communications .......................................................................................................... 10
2.6 RF Transmission Error Control................................................................................................... 10
2.7 Transmitter Power Management................................................................................................ 10
2.8 Network Configurations.............................................................................................................. 11
2.8.1 Point-to-Point Network Operation ........................................................................................... 11
2.8.2 Point-to-Multipoint Network Operation.................................................................................... 11
2.8.3 Multipoint Peer-to-Peer Network Operation............................................................................ 12
2.8.4 Tree-Routing System Operation ............................................................................................. 12
2.9 Full-Duplex Serial Data Communications................................................................................... 12
2.10 Channel Access.......................................................................................................................... 12
2.10.1 Polling Mode ........................................................................................................................... 13
2.10.2 CSMA Mode............................................................................................................................ 14
2.10.3 TDMA Modes .......................................................................................................................... 15
2.11 Point-to-Point and Point-to-Multipoint Networks......................................................................... 15
2.11.1 TDMA Throughput................................................................................................................... 16
2.11.2 Polling Throughput.................................................................................................................. 16
2.11.3 CSMA Throughput................................................................................................................... 17
2.11.4 Latency.................................................................................................................................... 18
2.11.5 Configuration Validation.......................................................................................................... 18
2.12 Tree-Routing Systems................................................................................................................ 20
2.12.1 Example Tree-Routing System............................................................................................... 20
2.12.2 Tree-Routing System Networks.............................................................................................. 22
2.12.3 Tree-Routing System Addressing........................................................................................... 23
2.12.4 Tree-Routing System Implementation Options....................................................................... 24
2.13 Serial Port Operation.................................................................................................................. 25
2.14 SPI Port Operation ..................................................................................................................... 26
2.15 Sleep Modes............................................................................................................................... 29
2.16 Encryption................................................................................................................................... 31
2.17 Synchronizing Co-located Bases ............................................................................................... 31
3.0 DNT900 Hardware......................................................................................................................... 32
3.1 Specifications ............................................................................................................................. 33
3.2 Module Interface......................................................................................................................... 34
3.3 DNT900 Antenna Connector...................................................................................................... 35
3.4 Input Voltages............................................................................................................................. 36
3.5 ESD and Transient Protection.................................................................................................... 36
3.6 Interfacing to 5 V Logic Systems................................................................................................ 36
3.7 Power-On Reset Requirements ................................................................................................. 37
3.8 Mounting and Enclosures........................................................................................................... 37
3.9 Labeling and Notices.................................................................................................................. 37

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4.0 Protocol Messages ........................................................................................................................ 39
4.1 Protocol Message Formats......................................................................................................... 39
4.1.1 Message Types....................................................................................................................... 39
4.1.2 Message Format Details ......................................................................................................... 40
4.1.3 /CFG Select Pin....................................................................................................................... 42
4.1.4 Flow Control ............................................................................................................................ 42
4.1.5 Protocol Mode Data Message Example.................................................................................. 42
4.1.6 Protocol Mode Tree-Routing MAC Address Discovery Example............................................ 43
4.2 Configuration Registers.............................................................................................................. 43
4.2.1 Bank 0 - Transceiver Setup..................................................................................................... 43
4.2.2 Bank 1 - System Settings........................................................................................................ 47
4.2.3 Bank 2 - Status Registers ....................................................................................................... 49
4.2.4 Bank 3 - Serial and SPI Settings............................................................................................. 51
4.2.5 Bank 4 - Host Protocol Settings .............................................................................................. 54
4.2.6 Bank 5 - I/O Peripheral Registers ........................................................................................... 55
4.2.7 Bank 6 - I/O Setup................................................................................................................... 56
4.2.8 Bank 7 - Authentication List .................................................................................................... 58
4.2.9 Bank 8 - Tree-Routing Active Router ID Table ....................................................................... 58
4.2.10 Bank 9 - Registered MAC Addresses ..................................................................................... 58
4.2.11 Bank FF - Special Functions................................................................................................... 59
4.2.12 Protocol Mode Configuration Message Example.................................................................... 60
4.2.13 Protocol Mode Sensor Message Example.............................................................................. 60
4.2.14 Protocol Mode Event Message Example................................................................................ 61
5.0 DNT900DK Developer’s Kit........................................................................................................... 62
5.1 DNT900DK Kit Contents............................................................................................................. 62
5.2 Additional Items Needed ............................................................................................................ 62
5.3 Developer’s Kit Operational Notes ............................................................................................. 62
5.4 Developer’s Kit Default Operating Configuration ....................................................................... 63
5.5 Developer’s Kit Hardware Assembly.......................................................................................... 63
5.6 DNT900 Demo Utility Program................................................................................................... 65
5.6.1 Initial Kit Operation.................................................................................................................. 66
5.6.2 Serial Communication and Radio Configuration..................................................................... 69
5.7 DNT900 Wizard Utility Program ................................................................................................. 76
5.8 DNT900 Interface Board Features ............................................................................................. 84
6.0 Demonstration Procedure.............................................................................................................. 87
7.0 Troubleshooting............................................................................................................................. 88
7.1 Diagnostic Port Commands........................................................................................................ 88
8.0 Appendices.................................................................................................................................... 91
8.1 Ordering Information................................................................................................................... 91
8.2 Technical Support....................................................................................................................... 91
8.3 DNT900 Mechanical Specifications............................................................................................ 92
8.4 DNT900 Development Board Schematic ................................................................................... 94
9.0 Warranty ........................................................................................................................................ 96

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1.0 Introduction
The DNT900 series transceivers provide highly reliable wireless connectivity for point-to-point, point-to-
multipoint, peer-to-peer or tree-routing applications. Frequency hopping spread spectrum (FHSS) tech-
nology ensures maximum resistance to multipath fading and robustness in the presence of interfering
signals, while operation in the 900 MHz ISM band allows license-free use in the US, Canada, South
America, Israel, Australia and New Zealand. The DNT900 supports all standard serial data rates for host
communications from 1.2 to 460.8 kb/s plus SPI data rates from 6.35 to 80.64 kb/s. On-board data buffer-
ing and an error-correcting radio protocol provide smooth data flow and simplify the task of integration
with existing applications. Key DNT900 features include:
•Multipath fading resistant frequency hop-
ping technology with up to 50 frequency
channels (902 to 928 MHz)
•Dynamic TDMA slot assignment that maxi-
mizes throughput and CSMA modes that
maximizes network size
•Support for point-to-point, point-to-
multipoint, peer-to-peer and
tree-routing networks
•AES encryption provides protection from
eavesdropping
•FCC 15.247 and IC RSS-210 certified for
license-free operation
•Nonvolatile memory stores DNT900 configu-
ration when powered off
•40 mile plus range with omni-directional
antennas (antenna height dependent)
•Selectable 1, 10, 100, 250, 500 or 1000 mW
transmit power with a firmware interlock of
85 mW maximum for 500 kb/s operation
•Transparent ARQ protocol with data
buffering ensures data integrity
•Simple interface handles both data and
control at up to 460.8 kb/s on the serial port
or 80.64 kb/s on the SPI port
•Analog and Digital I/O simplifies wireless
sensing
•Auto-reporting mode for I/O simplifies appli-
cation development
1.1 Why Spread Spectrum?
A radio 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 from
a phenomenon known as multipath fading. Multipath fading results when two or more reflected rays of the
transmitted signal arrive at the receiving antenna with opposing phases, thereby partially or completely
canceling the signal. This problem is particularly prevalent in indoor installations. In the frequency do-
main, a multipath fade can be described as a frequency-selective notch that shifts in location and intensity
over time as reflections change due to motion of the radio or objects within its range. At any given time,
multipath fades will typically occupy 1% - 2% of the band. From a probabilistic viewpoint, a conventional
radio system faces a 1% - 2% chance of signal impairment at any given time due to multipath fading.
Spread spectrum reduces the vulnerability of a radio system to both multipath fading and jammers by
distributing the transmitted signal over a larger region of the frequency band than would otherwise be
necessary to send the information. This allows the signal to be reconstructed even though part of it may
be lost or corrupted in transmission.

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Narrow-band versus spread-spectrum transmission
Figure 1.1.1
1.2 Frequency Hopping versus Direct Sequence
The two primary approaches to spread spectrum are direct sequence spread spectrum (DSSS) and
frequency hopping spread spectrum (FHSS), either of which can generally be adapted to a given applica-
tion. Direct sequence spread spectrum is produced by multiplying the transmitted data stream by a much
faster, noise-like repeating pattern. 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 narrow-band interference from multipath and jammers. Transmitting the data signal as usual, but
varying the carrier frequency rapidly according to a pseudo-random pattern over a broad range of chan-
nels produces a frequency hopping spectrum system.
Forms of spread spectrum - direct sequence and frequency hopping
Figure 1.1.2

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One disadvantage of direct sequence systems is that due to design issues related to broadband transmit-
ters and receivers, they generally employ only a minimal amount of spreading, often no more than the
minimum required by the regulating agencies. For this reason, the ability of DSSS systems to overcome
fading and in-band jammers is relatively weak. By contrast, FHSS systems are capable of hopping
throughout the entire band, statistically reducing the chances that a transmission will be affected by
fading or interference. This means that a FHSS system will degrade gracefully as the band gets noisier,
while a DSSS system may exhibit uneven coverage or work well until a certain point and then give out
completely.
Because it offers greater immunity to interfering signals, FHSS is often the preferred choice for co-located
systems. Since direct sequence signals are very wide, they can offer only a few non-overlapping chan-
nels, whereas multiple hoppers can interleave, minimizing interference. Frequency hopping systems do
carry some disadvantages, in that they require an initial acquisition period during which the receiver must
lock on to the moving carrier of the transmitter before any data can be sent, which typically takes several
seconds. In summary, frequency hopping systems generally feature greater coverage and channel utiliza-
tion than comparable direct sequence systems. Of course, other implementation factors such as size,
cost, power consumption and ease of implementation must also be considered before a final radio design
choice can be made.
DNT900 series modules achieve regulatory certification under FHSS rules at air data rates of 38.4, 115.2
and 200 kb/s. At 500 kb/s, the DNT900 series modules achieve regulatory certification under “digital
modulation”or DTS (DSSS) rules. At 500 kb/s DNT900 series modules still employ frequency hopping to
mitigate the effects of interference and multipath fading, but hop on fewer, more widely spaced frequen-
cies than at lower data rates.
2.0 DNT900 Radio Operation
2.1 Network Synchronization and Registration
As discussed above, frequency hopping spread spectrum radios such as the DNT900 periodically change
their transmit frequency. In order for the other radios in the network to receive the transmission, they must
be listening to the frequency on which the current transmission is being sent. To do this, all the radios in
the network must be synchronized to the same hopping pattern.
In all DNT900 networks, one radio is designated as the base. All other radios are designated as remotes
or routers. The base transmits a beacon each time it hops to a different frequency, which allows the other
radios in its network to synchronize with it. Since all radios in the network know the hopping pattern, once
they are synchronized with the base, they know which frequency to hop to and when.
When a remote or router is powered on, it rapidly scans the frequency band for the synchronizing signal.
Since the base is transmitting on up to 50 frequencies and the remotes and routers are scanning up to 50
frequencies, it can take several seconds to synchronize with the base.

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Once a radio has synchronized with the base, it will request registration information to allow it to join the
network. Registration is handled automatically by the base. When a radio is registered, it receives several
network parameters from the base, including HopDuration, InitialParentNwkID, FrequencyBand and
Nwk_Key (see Section 4.2 for parameter details). Note that if a registration parameter is changed at the
base, it will update the parameter in the remotes or routers over the air.
When leasing is enabled, registration also allows the base to track radios entering and leaving a network,
up to a limit of 126. The base builds a table of serial numbers of registered radios using their three-byte
MAC addresses. To detect if a radio has gone offline or out of range, a registration is leased and must be
renewed within the configured lease interval. DNT900 radios automatically send lease renewal request to
the base. There is nothing a remote host needs to do to keep the lease renewed. Note that more than
126 radios can join a network, but base-managed leasing cannot be used. In this case, the base can be
configured to send join announcements to a host application for an unlimited number of radios. The
application can then verify the continued presence of each radio in the network through periodic polling.
The DNT900 also supports a RemoteLeave command that allows a host application to release a radio
from the network. This is useful to remove any rogue radios that may have joined then network when
authentication is not being used. It is also useful to remove remotes from the network once they have
been serviced by the application. The RemoteLeave command includes the amount of time the radio
must leave the network, which can be set from 2 seconds to more than 36 hours. In addition, a radio can
be told to leave and not rejoin until it has been power-cycled or reset. The base can use RemoteLeave to
keep track of remotes that have not yet been serviced, allowing networks of more than 126 remotes to be
indirectly tracked by the base.
2.2 Authentication
In many applications it is desirable to control which radios can join a network. This provides security from
rogue radios joining the network and simplifies network segregation for co-located networks. Registration
is controlled by the AuthMode parameter in the base. The AuthMode parameter can be set to one of four
values, 0..3. The default value is 0, which allows any remote or router to register with a base.
When the AuthMode parameter is set to 1, a radio’s address must be listed in Parameter Bank 7 before it
will be allowed to register with the base. This is referred to as base authentication. Bank 7 must be pre-
loaded with the addresses of the authorized remotes before using base authentication. If a radio whose
MAC address is not in Bank 7 attempts to join the network the base will deny the registration request. A
maximum of 16 remotes can be entered into Bank 7. To support larger networks, mode 2 must be used.
When the AuthMode parameter is set to 2, the address of a radio attempting to register with the base is
sent to the host for authentication in a JoinRequest message. The host application determines if the radio
should be allowed to register and returns a JoinReply message to the base containing a PermitStatus
parameter that allows or blocks the radio from registering. The host application has 30 seconds in which
to respond, after which time the base denies registration to the radio. Up to 16 join requests can be
pending at any one time. If more than 16 radios are asking to join, the first 16 will be serviced and addi-
tional radios will be serviced after the earlier requests are handled. The RegDenialDelay parameter
controls how often a radio will request registration after it has been denied. If it is anticipated that more
than 16 radios will request registration before the application can service the first 16, this parameter
should be set to the time it will take the application to service four requests, as this will speed the authen-
tication process by freeing the base from issuing multiple denials to the same remotes.

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When the AuthMode parameter is set to 3, authentication is locked to the addresses of the radios cur-
rently registered with the base. Mode 3 is typically used in conjunction with Mode 0 during a commission-
ing process. AuthMode is set to 0, radios are turned on and allowed to register with the base, and
AuthMode is then switched to 3 to lock the network membership.
2.3 Serial Port Modes
DNT900 radios can work in two data modes on the primary serial (UART) port: transparent and packet
protocol. Transparent mode formatting is simply the raw user data. Protocol mode formatting includes a
start-of-packet framing character, length byte, addressing, command bytes, etc. Transparent mode opera-
tion is especially useful in point-to-point systems that act as simple cable replacements. In point-to-
multipoint, peer-to-peer and tree-routing systems where the base needs to send data specifically to each
radio, protocol formatting must be used unless the data being sent includes addressing information that
the devices connected to the remotes/routers can use to determine the intended destination of the broad-
cast data. Protocol formatting is also required for configuration commands and responses, and sensor I/O
commands and responses. Protocol mode can be used at the base while transparent mode is used at the
remotes. The one caution about protocol mode: the length of a protocol mode message cannot exceed
the BaseSlotSize or RemoteSlotSize or the packet will be discarded. Protocol formatting details are
covered in Section 4.
The DNT900 provides two ways to switch between transparent and protocol modes. To enter protocol
mode, the /CFG input Pin 18 can be switched from logic high to low, or the EnterProtocolMode command
can be sent. When input Pin 18 is switched from logic low to high, or an ExitProtocolMode command is
sent to the primary serial input, the DNT900 will switch to transparent operation. Note that it is possible
that part of the EnterProtocolMode command will be sent over the air as transparent data.
When operating in transparent mode, two configuration parameters control when a DNT900 radio will
send the data in its transmit buffer. The MinPacketLength parameter sets the minimum number of bytes
that must be present in the transmit buffer to trigger a transmission. The TxTimeout parameter sets the
maximum time data in the transmit buffer will be held before transmitting it, even if the number of data
bytes is less than MinPacketLength. The default value for MinPacketLength parameter is one and the
TxTimeout parameter is zero, so that any bytes that arrive in the DNT900 transmit buffer will be sent on
the next hop. As discussed in Section 2.8.2, it is useful to set these parameters to values greater than
their defaults in point-to-multipoint systems where some or all the remotes are in transparent mode.
2.4 SPI Port Modes
DNT900 radios can be configured to transmit and receive data through the serial peripheral interface
(SPI) port instead of the primary serial (UART) port. A DNT900 can operate as either an SPI Master or
Slave. Messages routed through the SPI port must be protocol formatted, as described in Section 4.
When a DNT900 is acting as an SPI Slave, all messages are routed through the SPI port. When a
DNT900 is acting as an SPI Master, only data messages are routed through the SPI port; radio configura-
tion commands and responses are routed through the primary serial (UART) port. A radio configured as
an SPI Master can use a command stored in the SPI_MasterCmdStr parameter to interrogate a Slave
peripheral for data to transmit to the base. This is especially useful where periodic I/O reporting is en-
abled on the remote. Alternately, the base can send an interrogation command to the radio to fetch pe-
ripheral data. SPI operation is configured with the SPI_Mode parameter.

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2.5 RF Data Communications
At the beginning of each hop the base transmits a beacon, which always includes a synchronizing signal.
After synchronization is sent, the base will transmit any user data in its transmit buffer, unless in transpar-
ent mode the MinPacketLength and/or TxTimeout parameters have been set above their default values.
The maximum amount of user data bytes that the base can transmit per hop is limited by the BaseSlot-
Size parameter, as discussed in Section 2.8.1. If there is no user data or reception acknowledgements
(ACKs) to be sent on a hop, the base will only transmit the synchronization signal in the beacon.
The operation for remotes and routers is similar to the base, but without a synchronizing signal. The
RemoteSlotSize parameter indicates the maximum number of user data bytes a remote or router can
transmit on one hop and is a read-only value. The RemoteSlotSize is determined by the HopDuration and
BaseSlotSize parameters and the number of registered radios. The MinPacketLength and TxTimeout
parameters operate in a remote in the same manner as in the base.
2.6 RF Transmission Error Control
The DNT900 supports two error control modes: automatic transmission repeats (ARQ), and redundant
transmissions for broadcast packets. In both modes, the radio will detect and discard any duplicates of
messages it receives so that the host application will only receive one copy of a given message. In the
redundant transmission mode, broadcast packets are repeated a fixed number of times based on the
value of the ARQ_AttemptLimit parameter. In ARQ mode, a packet is sent and an acknowledgement is
expected on the next hop. If an acknowledgement is not received, the packet is transmitted again on the
next available hop until either an ACK is received or the maximum number of attempts is exhausted. If the
ARQ_AttemptLimit parameter is set to its maximum value, a packet transmission will be retried without
limit until the packet is acknowledged. This is useful in some point-to-point cable replacement applications
where it is important that data truly be 100% error-free, even if the destination remote goes out of range
temporarily.
2.7 Transmitter Power Management
The DNT900 includes provisions for setting the base transmit power level and the remote maximum
transmit power level with the TxPower parameter. DNT900 networks covering a small area can be ad-
justed to run at lower transmitter power levels, reducing potential interference to other nearby systems.
Radios that are located close to their base can be adjusted to run at lower maximum power, further
reducing potential interference. Base units transmit at the fixed power level set by the TxPower parame-
ter. Remotes and routers automatically adjust their transmitter power to deliver packets to the base at an
adequate but not excessive signal level, while not transmitting more power than set by their TxPower
parameter. Remotes and routers make transmitter power adjustments using the strength of the signals
received from the base and the base transmitter power setting, which is periodically transmitted by the
base. The automatic transmit power adjustment is enabled by default, but can be disabled if so desired.
Refer to Section 4.2.1 for details.