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US Army and NATO standard audio and FILL connector
The U-229 is a standard military connector used by the US Army and by NATO
for connection of audio equipment to a radio (microphone, headset, etc.)
as well as for the connection of key fillers to cryptographic equipment (FILL).
The standard connector has 5 pins, marked A-E, but a 6-pin version also exists.
In the latter case, the extra pin is marked 'F' and is located at the center.
The image above shows the pinout when looking at the contacts of the
female connector (left) and male connector (right).
Many different versions of the connector and its mating receptacles are
available, such as 5 or 6-pin types, male or female and cable or panel mount.
Although each variant has its own specific type number, they are often referred
to as U-229. The table below shows the correct number for each version.
U-229/U is the female cable mount version.
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Type
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M/F
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Pins
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Description
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U-228/U
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M
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5
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5-pin, male, cable mount
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U-229/U
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F
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5
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5-pin, female, cable mount
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U-328/U
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M
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6
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6-pin, male, cable mount
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U-329/U
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F
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6
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6-pin, female, cable mount
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U-183/U
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M
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5
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5-pin, male, panel mount (chassis)
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U-283/U
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M
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6
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6-pin, male, panel mount (chassis)
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GC-429
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F
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5
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5-pin, female, circular panel mount (chassis)
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GC-629
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F
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5
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5-pin, female, square panel mount (chassis)
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GC-529
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F
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6
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6-pin, female, circular panel mount (chassis)
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GC-729
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F
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6
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6-pin, female, square panel mount (chassis)
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The U-229 was initially designed for use as an audio connector on military
radio equipment. The female cable part is commonly found on microphones,
speakers and handsets. In most cases the 5-pin version is used for this.
The radio itself usually has a 5-pin U-183/U male socket.
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The image on the right show a typical U-229/U female connector (right) as
part of a handset. On the left is the radio set which (in this case) has two
identical U-183 sockets. Most radios have two sockets to allow the separate
connection of a microphone and speaker. The NATO-standard
pinout of this connector is given below.
Note that not all radios adhere to this standard.
Some radios, such as the SINCGARS RT-1439,
use the 6-pin variant of the U-183 socket (U-283).
This allows the same socket to be used as a KEY FILL connector
(see below).
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Nearly all US Army and NATO equipment uses the same pinout for this
connector, so that all accessories are more or less compatible. The only
exception to this rule is the Dutch RT-3600 radio,
which has its microphone (MIC) and speaker (SPK) wires swapped.
The reason for this is currently unknown, but it
caused great problems when trying to connect standard accessories.
The table below shows both types of connection.
The NATO pinout is the more common one.
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Pin
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NATO
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RT-3600
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Description
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Note
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A
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GND
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GND
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Ground (common wire)
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B
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SPK
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MIC
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Speaker (microphone on the RT-3600)
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1
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C
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PTT
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PTT
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Push-to-Talk switch (connects to ground)
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2
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D
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MIC
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SPK
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Microphone (speaker on the RT-3600)
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E
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EXP
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-
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Various expansions. Not standardized.
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3
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F
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EXT
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-
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Not present on most radios.
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4
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- External speaker sense
Some radios have a +6V DC offset on this pin. It is used for sensing the presence
of an external speaker and (if it finds one) muting the internal speaker.
- Push To Talk bus (PTT)
This pin should be grounded when transmitting. It is neither an input nor an output,
but should be considered a BUS. Anyone on the bus could start a transmission by
asserting this line to ground. On some radios it is also used for CW (morse),
but this is not possible if the radio supports SSB. In the latter case, pin E is
used for CW.
- External power or fast CW
The function of pin E is not standardized, so different radios used it for different
purposes. On some radios, such as the PRC-68 family, it is used as a 12V power input.
Some manpack radios, such as the PRC-74 and PRC-104 use this pin for CW input (morse).
In such cases it can also be used for the connection of a high speed
burst encoder,
such as the GRA-71.
On other radios, pin E is used as an extra speaker line, or as a retransmission PTT
line in case of a repeater.
- Center pin
This pin is not present on the original U-229 connector. On some radios however
a 6-pin socket is mounted, to allow for future modifications and/or additional features.
Some radios use it for digital signals (e.g. uploading and downloading of channel
frequency assignments) and for retransmission PTT.
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The 5 or 6-pin version of the U-229 can also be used to connect a
key loader to
a crypto device,
or to a radio with built-in crypto and/or
frequency hopping (FH).
In many cases this is combined with the audio functionality described above.
Such is the case with many of the SINCGARS
radios.
The 6-pin version of the U-229/U (known as the U-329/U) is most commonly
used for FILL purposes, but this is not absolutely necessary, as the center pin
(F) is hardly ever used.
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The image on the right shows two 6-pin U-283 receptacles on the front panel of the
KY-57 voice encryption device. The rightmost one is for connection to a handset, whilst the leftmost one is free for the connection
of a key filler.
Any device that features a U-229 connector, should be designed in such
a way that it never causes any damage, even when connected to the wrong type
of equipment.
Modern SINCGARS radios uses the same
connector for audio, data and key-fill purposes.
Connecting a key filler to the wrong connector is an easy mistake.
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Generally speaking, there are two different protocols for transferring cryptographic
keys from a fill gun into a radio or crypto device. They are both developed by
the NSA. The oldest standard is DS-102,
which features synchronous data transfer at arbitrary speeds. It has gradually been
replaced by the newer DS-101 standard which is based on RS-232, but many modern devices
support both protocols on the same connector.
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DS-102
This is the oldest protocol used for key filling purposes. It describes the
physical specifications as well as the data flow. Unfortunately, DS-102 is not
yet in the public domain, so the description below is based on global observations
and other sources [1]. DS-102 is a synchronous protocol that requires separate
DATA and CLOCK signals. It uses negative logic signals, where a '0' is specified
as 0V and and logic '1' as -6V. The pinout is given in the table below.
The advantage of synchronous data communication is that it can be used at various
speeds (and even at varying speeds) without the need to configure the receiving
device accordingly. This was particularly useful when using the
KOI-18 key filler, which had a punched paper tape that was
manually pulled through the filler. Whilst doing so, the sprocket hole provided
the clock (CLK).
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Pin
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DS-102
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Description
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Note
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A
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GND
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Ground (common wire)
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B
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-
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Not used
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C
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ACK
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FILL request acknowlegment
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D
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DATA
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Fill data into radio or crypto device
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E
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CLK
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Fill clock into radio or crypto device
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F
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-
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-
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DS-101
This is the newer standard that replaces the earlier DS-102.
Like the DS-102 standard, it was developed by the NSA
and is not yet in the public domain.
DS-101 is an asynchronous protocol that is based on RS-232.
It has data input and ouput lines (RX/TX) plus handshaking (CTS/RTS).
Data rate, format and protocol are unknown at this time.
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Pin
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DS-101
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Description
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Note
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A
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GND
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Ground (common wire)
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B
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RTS
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Request to Send
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C
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RX
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Data out of radio or crypto device
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D
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TX
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Fill data into radio or crypto device
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E
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CTS
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Clear to Send
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F
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-
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-
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SINCGARS
Earlier SINCGARS radios,
such as the RT-1439,
feature a FILL connector that can be used to program the
Frequency Hopping (FH)
tables. This was done using specific devices such as the
MX-18290.
Voice encryption was achieved by using an additional device, such as the
KY-57
or the KY-99. Both these devices feature a special FILL connector
that is used to load the crypto keys by means of a
KYK-13 or similar.
Later SINCGARS radios had built-in COMSEC and allowed a KYK-13 to be connected
directly to the radio. The table below shows the pin assignment of the FILL
connector as specified in the SINCGARS documentation [1].
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Pin
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SINCGARS
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Description
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Note
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A
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GND
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Ground (common wire)
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B
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CCD
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Not used for fill
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C
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FILL REQ-N
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Fill request acknowledgment
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D
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FILL INFO
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Fill data into radio
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E
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FILL IA
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Fill info available
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F
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MUX
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MUX Override. Not used for fill
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The 6-pin version of the U-229/U (called U-329/U) is also used for DATA interfaces
on SINCGARS radios. Data can be send as
analog tones between 300 and 3000 Hz (slow speed, e.g. on HF) or as true digital
signals with a variety of baud rates between 75 baud and 16 kbit/s (ASYNC/SYNC).
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The image on the right shows the RT-1439
SINCGARS radio, which has two identical 6-pin connectors on its front panel.
One connector is marked AUDIO/FILL,
whilst the other one is marked AUDIO/DATA.
Although any analog audio device (e.g. a handset) can be connected to either connector,
they are completely different from a digital point of view.
The upper connector shares the FILL function and allows a key filler to be connected.
The lower connector shares the DATA interface and allows the connection of
a digital serial device.
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A rotary switch to the left of the lower AUDIO connector is used for selection of
the appropriate serial speed (baudrate). It can be set to a number of speeds between
75 and 4800 baud (4K8) in asychronous mode, or 16000 baud (16K) in synchronous mode.
When in synchronous mode, one of the pins of the connector carries the clock signal
(CLK). The table below shows the pinout of the connector in DATA mode.
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Pin
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SINCGARS
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Description
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Note
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A
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GND
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Ground (common wire)
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B
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RX
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Data from radio
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C
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PTT
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Grounded when transmitting
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D
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CLK
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Clock out (in synchronous mode)
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1
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E
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DIG
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Digital Data Model selected (when grounded)
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2
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F
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TX
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Data into radio
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3
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- Analog data input
In Analog mode, this pin is used as input for the data tones.
Analog mode is selected by grounding pin F.
This probably bypasses any filters in the audio path of the transceiver.
In synchronous digital data mode, this pin carries the clock signal (CLK).
- Digital data mode
The excact functionality of this pin is currently unknown.
Grounding this pin seems to select digital (data) mode.
When both pin E and F are high-impedant (default) analog voice mode is selected.
- Analog data mode
In digital mode, this pin is used as the DATA input (into the radio).
When pin F is grounded, analog data mode (i.e. tones) is selected.
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© Copyright 2009-2013, Paul Reuvers & Marc Simons. Last changed: Wednesday, 21 December 2011 - 14:57 CET
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