RFM DNT2400 Series Quick setup guide

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DNT2400 Series
2.4 GHz Spread Spectrum
Wireless Transceivers
Integration Guide

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Important Regulatory Information
RFM Product FCC ID: HSW-DNT2400
IC 4492A-DNT2400
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 DNT2400 has been designed to operate with any dipole antenna of up to 9 dBi of gain, or any patch
of up to 6 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
9 dB. Antennas not included in this list or having a gain greater than 9 dB are strictly prohibited for use
with this device. The required antenna impedance is 50 ohms:
RFM OMNI249 Omnidirectional Dipole Antenna, 9 dB
RFM PA2400 Patch Antenna, 6 dB
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 3.10 of this manual for regulatory notices and labeling requirements. Changes or modifica-
tions to a DNT2400 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 DNT2400 Radio Operation ................................................................................................................. 7
2.1 Network Synchronization and Registration...................................................................................... 7
2.2 Authentication.................................................................................................................................. 8
2.3 Transparent and Protocol Serial Port Modes .................................................................................. 9
2.4 RF Data Communications................................................................................................................ 9
2.5 RF Transmission Error Control........................................................................................................ 9
2.6 Transmitter Power Management ................................................................................................... 10
2.7 Network Configurations ................................................................................................................. 10
2.7.1 Point-to-Point Network Operation............................................................................................... 10
2.7.2 Point-to-Multipoint Network Operation ....................................................................................... 11
2.7.3 Peer-to-Peer Network Operation................................................................................................ 11
2.8 Full-Duplex Serial Data Communications...................................................................................... 11
2.9 Channel Access............................................................................................................................. 12
2.9.1 Polling Mode............................................................................................................................... 12
2.9.2 CSMA Mode ............................................................................................................................... 13
2.9.3 TDMA Modes.............................................................................................................................. 14
2.10 Transmission Configuration Planning............................................................................................ 14
2.10.1 TDMA Throughput...................................................................................................................... 15
2.10.2 Polling Throughput ..................................................................................................................... 15
2.10.3 CSMA Throughput...................................................................................................................... 16
2.10.4 Latency....................................................................................................................................... 16
2.10.5 Configuration Validation ............................................................................................................. 17
2.11 Serial Port Operation.................................................................................................................. 19
2.12 Sleep Modes.................................................................................................................................. 20
2.13 Encryption...................................................................................................................................... 22
2.14 Synchronizing Co-located Bases................................................................................................... 22
3.0 DNT2400 Hardware.......................................................................................................................... 24
3.1 Specifications................................................................................................................................. 25
3.2 Module Interface............................................................................................................................ 26
3.3 DNT2400C RFIO Stripline............................................................................................................. 27
3.4 DNT2400 Antenna Connector ....................................................................................................... 28
3.5 Input Voltages................................................................................................................................ 28
3.6 ESD and Transient Protection....................................................................................................... 28
3.7 Interfacing to 5 V Logic Systems................................................................................................... 29
3.8 Power-On Reset Requirements..................................................................................................... 29
3.9 Mounting and Enclosures .............................................................................................................. 29
3.10 Labeling and Notices ..................................................................................................................... 29
4.0 Protocol Messages............................................................................................................................ 31
4.1 Protocol Message Formats............................................................................................................ 31
4.1.1 Message Types .......................................................................................................................... 31
4.1.2 Message Format Details............................................................................................................. 32
4.1.3 /CFG Select Pin.......................................................................................................................... 33
4.1.4 Flow Control ............................................................................................................................... 33
4.1.5 Protocol Mode Data Message Example..................................................................................... 34

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4.2 Configuration Registers ................................................................................................................. 34
4.2.1 Bank 0 - Transceiver Setup........................................................................................................ 34
4.2.2 Bank 1 - System Settings........................................................................................................... 36
4.2.3 Bank 2 - Status Registers........................................................................................................... 39
4.2.4 Bank 3 - Serial............................................................................................................................ 41
4.2.5 Bank 4 - Host Protocol Settings ................................................................................................. 42
4.2.6 Bank 5 - I/O Peripheral Registers............................................................................................... 43
4.2.7 Bank 6 - I/O Setup...................................................................................................................... 43
4.2.8 Bank 7 - Authentication List........................................................................................................ 45
4.2.9 Bank FF - Special Functions ...................................................................................................... 46
4.2.10 Protocol Mode Configuration Message Example....................................................................... 46
4.2.11 Protocol Mode Sensor Message Example ................................................................................. 47
4.2.12 Protocol Mode Event Message Example ................................................................................... 47
5.0 DNT2400DK Developer’s Kit ............................................................................................................ 48
5.1 DNT2400DK Kit Contents.............................................................................................................. 48
5.2 Additional Items Needed................................................................................................................ 48
5.3 Developer’s Kit Operational Notes................................................................................................. 48
5.4 Developer’s Kit Default Operating Configuration........................................................................... 49
5.5 Developer’s Kit Hardware Assembly ............................................................................................. 49
5.6 DNT2400 Demo Utility Program.................................................................................................... 51
5.6.1 Initial Kit Operation ..................................................................................................................... 52
5.6.2 Serial Communication and Radio Configuration ........................................................................ 55
5.7 DNT2400 Wizard Utility Program................................................................................................... 61
5.8 DNT2400 Interface Board Features .............................................................................................. 69
6.0 Demonstration Procedure................................................................................................................. 72
7.0 Troubleshooting ................................................................................................................................ 73
7.1 Diagnostic Port Commands........................................................................................................... 73
8.0 Appendices ....................................................................................................................................... 76
8.1 Ordering Information...................................................................................................................... 76
8.2 Technical Support.......................................................................................................................... 76
8.3 DNT2400 Mechanical Specifications............................................................................................. 77
8.4 DNT2400 Development Board Schematic..................................................................................... 80
9.0 Warranty............................................................................................................................................ 82

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1.0 Introduction
The DNT2400 series transceivers provide highly reliable wireless connectivity for point-to-point, point-to-
multipoint and peer-to-peer applications. Frequency hopping spread spectrum (FHSS) technology en-
sures maximum resistance to multipath fading and robustness in the presence of interfering signals, while
operation in the 2.4 GHz ISM band allows license-free use world wide. The DNT2400 supports all stan-
dard serial data rates for host communications from 1.2 to 460.8 kb/s. On-board data buffering and an
error correcting radio protocol provide smooth data flow and simplify the task of integration with existing
applications. Key DNT2400 features include:
•Multipath fading resistant frequency hop-
ping technology with up to 37 frequency
channels per subband
•Dynamic TDMA slot assignment that maxi-
mizes throughput and CSMA modes that
maximizes network size
•Support for point-to-point or point-to-
multipoint applications
•AES encryption provides protection from
eavesdropping
•FCC 15.247, IC and ETSI certified for
license-free operation
•Nonvolatile memory stores DNT2400 con-
figuration when powered off
•10 mile plus range with omnidirectional
antennas (antenna height dependent)
•Selectable 1, 10 and 63 mW transmit power
levels
•Transparent ARQ protocol with data
buffering ensures data integrity
•Selectable RF data rates of 38.4, 115.2, 200
and 500 kb/s
•Analog and digital I/O simplifies wireless
sensing
•Auto-reporting I/O mode simplifies applica-
tion 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 frequency band than would otherwise be necessary to
send the information. This allows a signal to be reconstructed even though part of it may be lost or cor-
rupted 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 spread 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 does carry
some disadvantage, in that it requires 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 sec-
onds. In summary, frequency hopping systems generally feature greater coverage and channel utilization
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.
2.0 DNT2400 Radio Operation
2.1 Network Synchronization and Registration
As discussed above, frequency hopping spread spectrum radios such as the DNT2400 periodically
change the frequency at which they transmit. 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 point-to-point or point-to-multipoint networks, one radio module is designated as the base. All other
radios are designated as remotes. One of the responsibilities of the base is to transmit a synchronization
signal (beacon) to the remotes to allow them to synchronize with the base. Since the remotes know the
hopping pattern, once they are synchronized with the base, they know which frequency to hop to and
when. Every time the base hops to a different frequency, it immediately transmits a synchronizing signal.
When a remote is powered on, it rapidly scans the frequency band for the synchronizing signal. Since the
base is transmitting on up to 37 frequencies and the remote is scanning up to 37 frequencies, it can take
several seconds for a remote to synchronize with the base.
Once a remote 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 remote is registered, it receives
several network parameters from the base, including HopDuration, InitialNwkID, 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 over the air.
Among other things, registration allows the tracking of remotes entering and leaving a network, up to a
limit of 254 remotes. The base builds a table of serial numbers of registered remotes using their three-
byte serial numbers (MAC addresses). To detect if a remote has gone offline or out of range, the registra-
tion is “leased”and must be “renewed”once every 250 hops. Any transmission from a remote running on
a leased registration renews the lease with the base. If a remote does not transmit within 250 hops, the

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radio automatically renews the lease with the base. There is nothing the remote host needs to do to keep
the lease renewed. Note that more remotes can join the network but their entering and leaving the net-
work cannot be tracked by the base radio. The DNT2400 base can be configured to send join announce-
ments to a host application for an unlimited number of remotes. The application can then verify the con-
tinued presence of remotes in the network through periodic polling of each remote.
In addition, the DNT2400 supports a RemoteLeave command that allows a host application to cause a
remote to leave the network. This is useful to remove any rogue remotes that may have joined when
authentication is not being used. It is also useful to remove remotes from the network once they have
been serviced by the application. In this manner, the base can use the lease times to keep track of re-
motes that have not yet been serviced thereby allowing networks of more than 254 remotes to be tracked.
The RemoteLeave command includes the amount of time the remote must leave the network which can
be set from 2 seconds to more than 36 hours. In addition, a remote can be told to leave and not rejoin
until it has been power-cycled or reset.
2.2 Authentication
In many applications it is desirable to control which remote devices may join the network. This provides
security from rogue nodes joining the network and simplifies network segregation for co-located networks.
Network registration of remotes 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 to regis-
ter with a base.
When the AuthMode parameter is set to 1, a remote’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
preloaded with the addresses of the authorized remotes before using base authentication. If a remote
whose MAC address is not in Bank 7 attempts to join the network the base radio 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 remote attempting to register with the base is
sent to the host for authentication in a JoinRequest message. The host application determines if the
remote should be allowed to register and returns a JoinReply message to the base containing a Permit-
Status parameter that allows or blocks the remote from registering. The host application has 30 seconds
in which to respond, after which time the base denies registration to the remote. Up to 16 join requests
can be pending at any one time. If more than 16 remotes are asking to join, the first 16 will be serviced
and additional remotes will be serviced after the earlier requests are handled. The RegDenialDelay pa-
rameter controls how often a remote will request registration after it has been denied. If it is anticipated
that more than 16 remotes 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 authentication process by freeing the base from issuing multiple denials to the same remotes.
When the AuthMode parameter is set to 3, authentication is locked to the addresses of the remotes
currently registered with the base. Mode 3 is typically used in conjunction with Mode 0 during a commis-
sioning process. AuthMode is set to 0, remotes are turned on and allowed to register with the base, and
AuthMode is then switched to 3 to lock the network membership.

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2.3 Transparent and Protocol Serial Port Modes
DNT2400 radios can work in two serial port data modes: 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 operation is especially useful
in point-to-point systems that act as simple cable replacements. In point-to-multipoint systems where the
base needs to send data specifically to each remote, protocol formatting must be used unless the data
being sent includes addressing information that the devices connected to the remote radios can use to
determine the intended destination of the broadcast data. Protocol formatting is also required for configu-
ration commands and responses, and sensor I/O commands and responses. Protocol mode can be used
at the base radio while transparent mode is used at the remotes. The one caution about protocol mode is
that 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 DNT2400 provides two ways to switch between transparent and protocol modes. If /CFG input Pin 18
on the DNT2400 is switched from logic high to low, protocol mode is invoked. Or if the EnterProtocolMode
command is sent, the DNT2400 will switch to the protocol mode. When input Pin 18 is switched from logic
low to high, or an ExitProtocolMode command is sent to the primary serial input, the DNT2400 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 DNT2400 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 DNT2400 transmit buffer will be sent on
the next hop. As discussed in Section 2.7.2, 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 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 2.7.1. 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 is similar to the base, but without a synchronizing signal. The RemoteSlotSize
parameter indicates the maximum number of user data bytes a remote 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 remotes. The MinPacketLength and TxTimeout parameters operate in a
remote in the same manner as in the base.
2.5 RF Transmission Error Control
The DNT2400 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

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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.
2.6 Transmitter Power Management
The DNT2400 includes provisions for setting the base transmit power level and the remote maximum
transmit power level with the TxPower parameter. DNT2400 networks covering a small area can be
adjusted to run at lower transmitter power levels, reducing potential interference to other nearby systems
such as 802.11 networks. Remotes 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 parameter. Remotes 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 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 remote automatic transmit power adjustment is enabled by default but can be disabled if so
desired. Refer to Section 4.2.1 for details.
2.7 Network Configurations
The DNT2400 supports three network configurations: point-to-point, point-to-multipoint, and peer-to-peer.
In a point-to-point network, one radio is set up as the base and the other radio is set up as a remote. In a
point-to-multipoint network, a star topology is used with the radio set up as a base acting as the central
communications point and all other radios in the network set up as remotes. In this configuration, each
communication takes place between the base and one of the remotes. Peer-to-peer communications
between remotes using the base as a relay is also supported, as discussed in Section 2.7.3.
2.7.1 Point-to-Point Network Operation
Most point-to-point networks act as serial cable replacements and both the base and the remote use
transparent mode. Unless the MinPacketLength and TxTimeout parameters have been set above their
default values, the base will send the data in its transmit buffer on each hop, up to a limit controlled by the
BaseSlotSize parameter. In transparent mode, if the base is buffering more data than can be sent on one
hop, the remaining data will be sent on subsequent hops. The base adds the address of the remote, a
packet sequence number and error checking bytes to the data when it is transmitted. These additional
bytes are not output at the remote in transparent mode. The sequence number is used in acknowledging
successful transmissions and in retransmitting corrupted transmissions. A two-byte CRC and a one-byte
checksum allow a received transmission to be checked for errors. When a transmission is received by the
remote, it will be acknowledged if it checks error free. If no acknowledgment is received, the base will
retransmit the same data on the next hop. Note that acknowledgements from remotes are suppressed on
broadcast packets from the base.