Murata WIT2420 Quick setup guide

WIT2420
2.4GHz Spread Spectrum
Wireless Industrial Transceiver
Integration Guide
June 2nd 2021
Note: This unit has been tested and found to
comply with the limits for a class Adigital 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
instruction 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 his
own expense.

The modular transmitter is only FCC authorized for the specific rule parts listed on the grant;
when it is installed in a host device, the host product manufacturer is responsible for
compliance to any other FCC rules that apply to the host not covered by the modular
transmitter grant of certification. The final host product still requires Part 15 Subpart B
compliance testing with the modular transmitter installed.
If the WIT2420 is installed within another device the outside of the device into which the
WIT2420 is installed must also display a label referring to the enclosed module. The label
required for the WIT2420 module is as follows: Contains FCC ID: HSW-2420 and Contains
IC: 4492A-2420.
This device complies with Part 15 of the FCC Rules. Operation is subject to the following two
(1) This device may not cause harmful interference, and (2) this device must accept any
interference received, including inerference that may cause undesired operation.
WARNING: changes not expressly approved by the party responsible for compliance could
void the user’s authority to operate this device.
WARNING: a 20cm separation distance must be maintained between this device and the user.
This device complies with Industry Canada license-exempt RSS standard(s). Operation is
subject to the following two conditions: (1) this device may not cause interference, and (2) this
device must accept any interference, including interference that may cause undesired operation
of the device. Le présent appareil est conforme aux CNR d'Industrie Canada applicables aux
appareils radio exempts de licence. L'exploitation est autorisée aux deux conditions suivantes :
(1) l'appareil ne doit pas produire de brouillage, et (2) l'utilisateur de l'appareil doit accepter
tout brouillage radioélectrique subi, même si le brouillage est susceptible d'en compromettre le
fonctionnement.
About This Manual
This manual is designed to allow integration of the Murata WIT2420 OEM module into
complete products. Care has been taken to try and make sure all of the information in this
manual is accurate. However, specifications can change over time and Murata cannot
guarantee the accuracy of this information. If you have any questions on any information in
this manual, please contact Murata Technical Support at [phone].

TABLE OF CONTENTS
1. INTRODUCTION ...................................................................................................................................................1
1.1 Why Spread Spectrum?...................................................................................................................................1
1.2 Frequency Hopping vs. Direct Sequence ........................................................................................................2
2. RADIO OPERATION.............................................................................................................................................4
2.1. Synchronization and Registration ..................................................................................................................4
2.2. Data Transmission .........................................................................................................................................5
2.2.1. Point-to-Point.......................................................................................................................................5
2.2.2. Point-to-Multipoint................................................................................................................................6
2.2.3. TDMA Mode.........................................................................................................................................6
2.2.4. Full Duplex Communication.................................................................................................................8
2.2.5. Error-free Packet Transmission Using ARQ........................................................................................8
2.3. Modes of Operation........................................................................................................................................9
2.3.1. Control and Data Modes......................................................................................................................9
2.3.2. Sleep Mode..........................................................................................................................................9
2.3.3. Low Power Mode and Duty Cycling.................................................................................................. 10
2.3.4. RF Flow Control Mode....................................................................................................................... 10
3. PROTOCOL MODES ......................................................................................................................................... 11
3.1. Packet Formats........................................................................................................................................... 13
3.1.1. Data Packet ...................................................................................................................................... 13
3.1.3. Connect Packet................................................................................................................................. 14
3.1.4. Disconnect Packet (base only, receive only)................................................................................... 14
4. MODEM INTERFACE ........................................................................................................................................ 15
4.1. Interfacing to 5 Volt Systems ...................................................................................................................... 16
4.2 Evaluation Unit and OEM Module Differences............................................................................................ 16
4.3 Three Wire Operation.................................................................................................................................. 16
4.4 Power-On Reset Requirements.................................................................................................................. 17
5. MODEM COMMANDS ....................................................................................................................................... 18
5.1. Serial Commands........................................................................................................................................ 18
5.2. Network Commands.................................................................................................................................... 19
5.3. Protocol Commands.................................................................................................................................... 21
5.4. Status Commands....................................................................................................................................... 24
5.5. Memory Commands.................................................................................................................................... 25
5.6. Modem Command Summary...................................................................................................................... 26
6. WIT2420 DEVELOPER’S KIT ............................................................................................................................ 27
6.1. COM24/WinCOM24 .................................................................................................................................... 27
6.2. Demonstration Procedure........................................................................................................................... 28
6.3. Troubleshooting .......................................................................................................................................... 29
7. APPENDICES..................................................................................................................................................... 31
7.1. Technical Specifications.............................................................................................................................. 31
7.1.1 Ordering Information.......................................................................................................................... 31
7.1.2. Power Specifications ........................................................................................................................ 31
7.1.3. RF Specifications.............................................................................................................................. 31
7.1.4. Mechanical Specifications ................................................................................................................ 31
7.2. Serial Connector Pinouts ............................................................................................................................ 32
7.3. Approved Antennas..................................................................................................................................... 32
7.4. Technical Support ....................................................................................................................................... 32
7.5. Reference Design ....................................................................................................................................... 33
7.6. Mechanical Drawing......................................................................................Error! Bookmark not defined.
7.7. Warranty........................................................................................................Error! Bookmark not defined.

© 1999, 2000 MurataCorporation 1 01/11/00
1. INTRODUCTION
The WIT2420 radio transceiver provides reliable wireless connectivity for either
point-to-point or multipoint applications. Frequency hopping spread spectrum technology
ensures maximum resistance to noise and multipath fading and robustness in the presence of
interfering signals, while operation in the 2.4GHz ISM band allows license-free use and
worldwide compliance. A simple serial interface supports asynchronous data up to 230400
bps. An on-board 3 KB buffer and an error-correcting over-the-air protocol provide smooth
data flow and simplify the task of integration with existing applications.
-Multipath fading impervious
frequency hopping technology
with 75 frequency channels
(2401-2475 MHz).
- Supports point-to-point or
multipoint applications.
- Meets FCC rules 15.247 and ETS
300.328 for worldwide license-
free operation.
- Superior range to 802.11 wireless
LAN devices.
- Transparent ARQ protocol
w/3KB buffer ensures data
integrity.
- Digital addressing supports up to
64 networks, with 62 remotes per
network.
- Low power 3.3v CMOS signals
- Simple serial interface handles both
data and control at up to 230400
bps.
- Fast acquisition typically locks to
hopping pattern in 2 seconds or less.
- Selectable 10 mW or 100 mW
transmit power.
- Support for diversity antenna.
- Built-in data scrambling reduces
possibility of eavesdropping.
- Nonvolatile memory stores
configuration when powered off.
- Smart power management features
for low current consumption.
- Dynamic TDMA slot assignment
that maximizes throughput.
1.1 Why Spread Spectrum?
The radio transmission channel is very hostile, corrupted by noise, path loss and
interfering transmissions from other radios. Even in a pure interference-free
environment, radio performance faces serious degradation through 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 phase, thereby
partially or completely canceling the desired signal. This is a problem particularly
prevalent in indoor installations. In the frequency domain, 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 2.4 GHz band. This means
that from a probabilistic viewpoint, a conventional radio system faces a 1% - 2% chance
of signal impairment at any given time due to multipath.

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Spread spectrum reduces the vulnerability of a radio system to both interference from
jammers and multipath fading 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
transit.
Figure 1
Narrowband vs. spread spectrum in the presence of interference
1.2 Frequency Hopping vs. Direct Sequence
The two primary approaches to spread spectrum are direct sequence (DS) and frequency
hopping (FH), either of which can generally be adapted to a given application. 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 baseband 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 varying the carrier frequency
rapidly according to a pseudo-random pattern over a broad range of channels produces a
frequency hopping spectrum system.

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Figure 2
Forms of spread spectrum
One disadvantage of direct sequence systems is that due to spectrum constraints and the
design difficulties of broadband receivers, they generally employ only a minimal amount
of spreading (typically no more than the minimum required by the regulating agencies).
For this reason, the ability of DS systems to overcome fading and in-band jammers is
relatively weak. By contrast, FH systems are capable of probing the entire band if
necessary to find a channel free of interference. Essentially, this means that a FH
system will degrade gracefully as the channel gets noisier while a DS 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, FH is often the preferred
choice for co-located systems. Since direct sequence signals are very wide, they tend to
offer few non-overlapping channels, whereas multiple hoppers may interleave with less
interference. Frequency hopping does carry some disadvantage in that as the transmitter
cycles through the hopping pattern it is nearly certain to visit a few blocked channels
where no data can be sent. If 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
can be found. A second consideration of frequency hopping systems is 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
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.
As an additional benefit, RF spectrum has been set aside at 2.4 GHz in most countries
(including the U.S.) for the purpose of allowing compliant spread spectrum systems to
operate freely without the requirement of a site license. This regulatory convenience
alone has been a large motivation for the industry-wide move toward spread spectrum.

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2. RADIO OPERATION
2.1. Synchronization and Registration
As discussed above, frequency hopping radios 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 over which the current transmission is being sent. To do
this, all the radios in the net must be synchronized and must be set to the same hopping
pattern. All radios in a net must be set to the same hopping pattern before attempting to
communicate.
In point-to-point or point-to-multipoint arrangements, one radio module is designated as the
base station. All other radios are designated remotes. One of the responsibilities of the base
station is to transmit a synchronization signal to the remotes to allow them to synchronize
with the base station. Since the remotes know the hopping pattern, once they are
synchronized with the base station, they know which frequency to hop to and when. Every
time the base station 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 station is transmitting over 75 frequencies and the remote is scanning
75 frequencies, it can take several seconds for a remote to synch up with the base station.
Once a remote has synchronized with the base station, it must request registration from the
base station. The registration process identifies to the base station the remotes from which
transmissions will be received and not discarded. Registration also allows tracking of
remotes entering and leaving the network. The base station builds a table of serial numbers
of registered remotes. To improve efficiency, the 24-bit remote serial number is assigned a
6-bit “handle” number. Two of these are reserved for system use, thus each base station can
register 62 separate remotes. This handle is how user applications will know the remotes. If
necessary, the automatic handle assignment can be overridden to explicitly tie certain handles
to certain remotes. See the section on Network Commands for details on the Set Default
Handle command.
To detect if a remote has gone offline or out of range, the registration must be “renewed”
once every 256 hops. Registration is completely automatic and requires no user application
intervention. When the remote is registered, it will receive several network parameters from
the base. This allows the base to automatically update these network parameters in the
remotes over the air. Once a parameter has been changed in the base, it is automatically
changed in the remotes. The parameters automatically changed are hop duration and the
duty cycle.
At the beginning of each hop, the base station transmits a synchronizing signal. After the
synchronizing signal has been sent, the base will transmit any data in its buffer unless data
transmit delay has been set. The data transmit delay parameter allows for the transmission
of groups of continuous data in transparent mode (protocol mode 0). The amount of data that

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the base station can transmit per hop is determined by the base slot size parameter. The
maximum amount of data sent by a base station per hop is 192 bytes. If there is no data to be
sent, the base station will not transmit until the next frequency.
The operation for remotes is similar to the base station without the synchronizing signal. The
amount of data a remote can send on one hop is dependent upon the hop duration, the base
slot size and the number of registered remotes. 212 bytes per hop is the maximum data length
a remote can transmit per hop, subject to limitations imposed by the hop duration, the base
slot size and the number of registered remotes. A detailed explanation of this relationship is
provided in Section 2.2.3. Minimum data length and data transmit delay operate the same as
with the base station.
Except for the registration process which occurs only when a remote logs onto the network,
the whole procedure is repeated on every frequency hop. Refer to the section on Modem
Commands for complete details on parameters affecting the transmission of data.
2.2. Data Transmission
The WIT2420 supports two network configurations: point-to-point and point-to-multipoint.
In a point-to-point network, one radio is set up as the base station 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 station acting as the central communications point and all other radios in the network
set up as remotes. In this configuration, all communications take place between the base
station and any one of the remotes. Remotes cannot communicate directly with each other.
It should be noted that point-to-point mode is a subset of point-to-multipoint mode and
therefore there is no need to specify one mode or the other.
2.2.1. Point-to-Point
In point-to-point mode, unless data transmit delay or minimum data length have been set, the
base station will transmit whatever data is in its buffer limited to 192 bytes or as limited by
the base slot size. If the base station has more data than can be sent on one hop, the
remaining data will be sent on subsequent hops. In addition to the data, the base station adds
some information to the transmission over the RF link. It adds the address of the remote to
which it is transmitting, even though in a point-to-point mode there is only one remote. It
also adds a sequence number to identify the transmission to the remote. This is needed in the
case of acknowledging successful transmissions and retransmitting unsuccessful
transmissions. Also added is a 24-bit CRC to allow the base to check the received
transmission for errors. When the remote receives the transmission, it will acknowledge the
transmission if it was received without errors. If no acknowledgment is received, the base
station will retransmit the same data on the next frequency hop.
In point-to-point mode, a remote will transmit whatever data is in its buffer up to the limit of
its maximum data length. If desired, minimum data length and data transmit delay can also
be set, which force the remote to wait until a certain amount of data is available or the

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specified delay is exceeded before transmitting. If the remote has more data than can be sent
on one hop, it will send as much data as possible as a packet, adding its own address, a
packet sequence number and 24-bit CRC. These additional bytes are transparent to the user
application if the protocol mode is 00 (which is the default). In the event a remote has more
data to send, the data will be sent on subsequent hops. If the transmission is received by the
base station without errors, the base station will acknowledge the transmission. If the remote
does not receive an acknowledgment, it will retransmit the data on the next frequency hop.
To the user application, acknowledgments and retransmissions all take place behind the
scenes without the need for user intervention.
2.2.2. Point-to-Multipoint
In point-to-multipoint mode, data sent from the user application to the base station must be
packetized by the user application unless the remote device can distinguish between
transmissions intended for it and transmissions intended for other remote devices. This is
necessary to identify the remote to which the base station should send data. When the user
packet is received by the remote, if the remote is in transparent mode (protocol mode 0), the
packetization bytes are stripped by the remote. In this instance the remote host receives just
data. If the remote is not in transparent mode, the remote host will receive the appropriate
packet header as specified by the remote’s protocol mode. Refer to the section Protocol
Modes for details on the various packet formats.
When a remote sends data to a base station in point-to-multipoint mode, the remote host does
not need to perform any packetization of the data. Remotes can operate in transparent mode
even though the base is operating in a packet mode. The remote will add address, sequence
and CRC bytes as in the point-to-point mode. When the base station receives the data, the
base station will add packetization header bytes according to its protocol mode setting.
2.2.3. TDMA Mode
For applications needing guaranteed bandwidth availability, the TDMA mode of the
WIT2420 can meet this requirement. In TDMA mode, each remote has an assigned time slot
during which it can transmit. The base station time slot is set independently of the remote
time slots through the Set Base Slot Size command. The base station assigns each remote a
time slot and informs the remotes of the size of the time slot. All remote time slots are the
same size that is determined by the number of remotes registered with the base station. The
slot size is a dynamic variable that changes as the number of registered remotes changes.
The remotes are continually updated with the time slot size. This approach continually
maximizes the data throughput. The base station divides the amount of time available per
hop by the number of registered remotes up to a maximum of 16 times slots per hop. If the
number of registered remotes is greater than 16, the time slots will be spread across the
required number of hops. For networks with more than 16 possible remotes, the Set Duty
Cycle command must be used to specify a duty cycle -- the number of hops over which the
time slots must be spread. For 1 to 16 remotes, no duty cycle is required; for 17 to 32
remotes a duty cycle of at least ½ is required; and for 33 to 62 remotes a duty cycle of ¼ or

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more is necessary. An added benefit of using the power save mode to set a duty cycle is
improved average current consumption efficiency. Refer to the Status Commands section for
details of this command.
When setting up a TDMA network, keep in mind that time slot length, maximum packet size
and hop duration are all interrelated. The hop duration parameter will determine the time
slot size and the maximum amount of data that can be transmitted per hop by the remotes.
There is a hard limit of the absolute maximum amount of data that can be sent on any given
hop of 212 bytes regardless of any parameters. The base station requires 1.7 ms overhead for
tuning, the synchronization signal and parameter updating, as well as a guard time of 500s
between each remote slot. Thus the amount of time allocated per remote slot is roughly:
hop duration –base slot –1.7ms - ( # of registered remotes-1)∙500s
( # of registered remotes)
Take for example a network comprised of a base station and 10 remotes. A hop duration of
10 ms is chosen. We decide that the base station needs to be able to send up to 32 bytes each
hop (equivalent to a capacity for the base of ~ 32 kbps). Counting the 1.7 ms overhead for
the base packet and making use of the fact that our RF rate is 460.8 kbps, we determine that
the base slot requires approximately:
Each remote time slot will be:
10 ms –2.3 ms –(9)∙0.5 ms
10
From our RF data rate of 460.8kbps we see that it takes 17.36 s to send a byte of data, so
each remote will be able to send up to
= 18 bytes of data per hop.
Note that the 18 bytes is the actual number of data bytes that can be sent. If the WIT2420 is
using a protocol mode, the packet overhead does not need to be considered. So in this
example, the total capacity per remote would be:
If we figure a minimum margin of safety for lost packets and retransmissions of about 20%,
we see that this would be more than sufficient to support 14.4 kbps of continuous data per
remote. It is also useful to remember that the asynchronous data input to the WIT2420 is
stripped of its start and stop bits during transmission by the radio, yielding a "bonus" of 10/8
or 25% in additional capacity.
= 0.32 ms
0.32 ms
17.36s
us
32∙8
460.8kbps
+ 1.7 ms = 2.3 ms
18 bytes
10 ms
= 18 kbps