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<li><a href="/"><h1>Chrisoft</h1></a></li>
<li><a href="/blog"><h2>Blog</h2></a></li>
<li><a href="#"><h3 id="title">R-BUS Technical Information</h3></a></li>
<li><span>Tags</span>
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<li><a href="/blog/list/music/">music</a></li><li><a href="/blog/list/electronics/">electronics</a></li></ul>
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<span>Table of Contents</span>
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<li><a class="toctarg" href="#tocanch0">Background</a></li><li><a class="toctarg" href="#tocanch1">Devices with R-BUS support</a></li><li><a class="toctarg" href="#tocanch2">Pin definition</a></li><li><a class="toctarg" href="#tocanch3">Official cable wiring</a></li><li><a class="toctarg" href="#tocanch4">Electrical
characteristics of the interface</a></li><li><ul class="tocnode"><li><a class="toctarg" href="#tocanch5">Power</a></li><li><a class="toctarg" href="#tocanch6">Digital Audio</a></li><li><a class="toctarg" href="#tocanch7">MIDI</a></li></ul></li></ul>
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<h2 id="titleh" class="TText" style="font-wight:normal;">R-BUS Technical Information</h2>
<div id="datetags" class="TText" style="margin-bottom:1em;">2024-02-02<br>#music #electronics</div>
<hr><div id="article" class="TText">
<article>
<h2 id="tocanch0" class="tvis">Background</h2>
<p>R-BUS (also called RMDB2 / RMDB II on older products) is an obsolete
proprietary interconnect format that carries bidirectional MIDI and
digital audio data created by Roland. It was used on Roland products
released from the late 90s to early 2000s.</p>
<p>There was a physically incompatible and much rarer predecessor of
R-BUS called RMDB (Roland Multipurpose Digital Bus). RMDB is not the
subject of this article.</p>
<p>Much of the information here is gathered from schematics inside
service manuals for various Roland products, mainly the XV-5080 and
VS-2400. These can be easily found with a search through the
interwebz.</p>
<p>This article assumes minimal electronics knowledge from the reader.
As a matter of fact, the author is also a layperson in this space.
Report of any issues in the article would be appreciated.</p>
<p>For other R-BUS related stuff on this website, please visit <a href="/rbusif">this page</a>.</p>
<h2 id="tocanch1" class="tvis">Devices with R-BUS support</h2>
<p>Here is a not necessarily complete list of Roland products that comes
with at least one R-BUS connector:</p>
<ul>
<li>Mixing Console
<ul>
<li>VM-3100Pro</li>
<li>VM-7100 / VM-7200 (3 ports on optional VM-24E I/O expansion)</li>
</ul></li>
<li>Studio Workstation
<ul>
<li>VS-2400</li>
<li>VS-2480 (2 ports)</li>
<li>VSR-880</li>
</ul></li>
<li>Production Studio
<ul>
<li>MV-8000 / MV-8800 (available through the MV8-OP1 audio I/O
expansion)</li>
</ul></li>
<li>Synthesizer
<ul>
<li>XV-5080 (output only)</li>
</ul></li>
<li>Interface Modules
<ul>
<li>RPC-1 (Conventional PCI R-BUS interface)</li>
<li>ADA-7000 (A/D converter)</li>
<li>AE-7000 (R-BUS <=> AES/EBU converter)</li>
<li>DIF-AT (R-BUS <=> TDIF & ADAT converter)</li>
<li>DIF-AT24 (R-BUS to ADAT and MIDI interface, 24-bit)</li>
</ul></li>
</ul>
<h2 id="tocanch2" class="tvis">Pin definition</h2>
<p>Connection for VS-2400 and XV-5080 is extracted from their respective
service manuals. Pin usage inferred from these connections.</p>
<table>
<colgroup>
<col style="width: 13%">
<col style="width: 31%">
<col style="width: 31%">
<col style="width: 22%">
</colgroup>
<thead>
<tr class="header">
<th style="text-align: center;">PIN</th>
<th style="text-align: center;">VS-2400</th>
<th style="text-align: center;">XV-5080</th>
<th style="text-align: left;">Usage</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: center;">1</td>
<td style="text-align: center;">+5V</td>
<td style="text-align: center;">+5V</td>
<td style="text-align: left;">Power output</td>
</tr>
<tr class="even">
<td style="text-align: center;">2</td>
<td style="text-align: center;">RBOUT11</td>
<td style="text-align: center;">SDO4</td>
<td style="text-align: left;">Channel 1/2 output (<span style="text-decoration: overline;">SDOUT1</span><a id="n1" href="#note1" class="note">[1]</a>)</td>
</tr>
<tr class="odd">
<td style="text-align: center;">3</td>
<td style="text-align: center;">RBOUT12</td>
<td style="text-align: center;">SDO5</td>
<td style="text-align: left;">Channel 3/4 output (<span style="text-decoration: overline;">SDOUT2</span>)</td>
</tr>
<tr class="even">
<td style="text-align: center;">4</td>
<td style="text-align: center;">RBOUT13</td>
<td style="text-align: center;">SDO6</td>
<td style="text-align: left;">Channel 5/6 output (<span style="text-decoration: overline;">SDOUT3</span>)</td>
</tr>
<tr class="odd">
<td style="text-align: center;">5</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="even">
<td style="text-align: center;">6</td>
<td style="text-align: center;">RBOUT14</td>
<td style="text-align: center;">SDO7</td>
<td style="text-align: left;">Channel 7/8 output (<span style="text-decoration: overline;">SDOUT4</span>)</td>
</tr>
<tr class="odd">
<td style="text-align: center;">7</td>
<td style="text-align: center;">NC <a id="n2" href="#note2" class="note">[2]</a></td>
<td style="text-align: center;">NC</td>
<td style="text-align: left;">Unused?</td>
</tr>
<tr class="even">
<td style="text-align: center;">8</td>
<td style="text-align: center;">RBIN14</td>
<td style="text-align: center;">NC</td>
<td style="text-align: left;">Channel 7/8 input (<span style="text-decoration: overline;">SDIN4</span>)</td>
</tr>
<tr class="odd">
<td style="text-align: center;">9</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="even">
<td style="text-align: center;">10</td>
<td style="text-align: center;">RBIN13</td>
<td style="text-align: center;">NC</td>
<td style="text-align: left;">Channel 5/6 input (<span style="text-decoration: overline;">SDIN3</span>)</td>
</tr>
<tr class="odd">
<td style="text-align: center;">11</td>
<td style="text-align: center;">RBIN12</td>
<td style="text-align: center;">NC</td>
<td style="text-align: left;">Channel 3/4 input (<span style="text-decoration: overline;">SDIN2</span>)</td>
</tr>
<tr class="even">
<td style="text-align: center;">12</td>
<td style="text-align: center;">RBIN11</td>
<td style="text-align: center;">SDI2</td>
<td style="text-align: left;">Channel 1/2 input (<span style="text-decoration: overline;">SDIN1</span>)</td>
</tr>
<tr class="odd">
<td style="text-align: center;">13</td>
<td style="text-align: center;">NC</td>
<td style="text-align: center;">NC</td>
<td style="text-align: left;">Power reception for bus-powered devices
<a id="n3" href="#note3" class="note">[3]</a></td>
</tr>
<tr class="even">
<td style="text-align: center;">14</td>
<td style="text-align: center;">PC_TXD1</td>
<td style="text-align: center;">RBUS_TX</td>
<td style="text-align: left;">MIDI transmit <a id="n4" href="#note4" class="note">[4]</a></td>
</tr>
<tr class="odd">
<td style="text-align: center;">15</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="even">
<td style="text-align: center;">16</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="odd">
<td style="text-align: center;">17</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="even">
<td style="text-align: center;">18</td>
<td style="text-align: center;">1FS</td>
<td style="text-align: center;">LRCK4</td>
<td style="text-align: left;">Frame sync (word clock) output</td>
</tr>
<tr class="odd">
<td style="text-align: center;">19</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="even">
<td style="text-align: center;">20</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="odd">
<td style="text-align: center;">21</td>
<td style="text-align: center;">RBFS1</td>
<td style="text-align: center;">RBUS-WDCLK</td>
<td style="text-align: left;">Frame sync (word clock) input</td>
</tr>
<tr class="even">
<td style="text-align: center;">22</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="odd">
<td style="text-align: center;">23</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="even">
<td style="text-align: center;">24</td>
<td style="text-align: center;">GND</td>
<td style="text-align: center;">GND</td>
<td style="text-align: left;">Ground</td>
</tr>
<tr class="odd">
<td style="text-align: center;">25</td>
<td style="text-align: center;">PC_RXD1</td>
<td style="text-align: center;">RBUS_RX</td>
<td style="text-align: left;">MIDI receive <a id="n5" href="#note5" class="note">[5]</a></td>
</tr>
</tbody>
</table>
<h2 id="tocanch3" class="tvis">Official cable wiring</h2>
<p>Roland has only disclosed partial information on the wiring scheme
used by the official R-BUS cables. <a id="n6" href="#note6" class="note">[6]</a>
However, it’s rather easy to infer the full wiring scheme from that
information. This has been confirmed by other third-party sources.
<a id="n7" href="#note7" class="note">[7]</a> <a id="n8" href="#note8" class="note">[8]</a></p>
<table>
<colgroup>
<col style="width: 25%">
<col style="width: 18%">
<col style="width: 11%">
<col style="width: 18%">
<col style="width: 25%">
</colgroup>
<thead>
<tr class="header">
<th style="text-align: right;">Usage 🖙</th>
<th style="text-align: center;">Pin on one side</th>
<th style="text-align: center;">is connected to</th>
<th style="text-align: center;">Pin on the other side</th>
<th style="text-align: left;">🖘 Usage</th>
</tr>
</thead>
<tbody>
<tr class="odd">
<td style="text-align: right;">+5V</td>
<td style="text-align: center;">1</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">13</td>
<td style="text-align: left;">+5V In</td>
</tr>
<tr class="even">
<td style="text-align: right;">SDOUT1</td>
<td style="text-align: center;">2</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">12</td>
<td style="text-align: left;">SDIN1</td>
</tr>
<tr class="odd">
<td style="text-align: right;">SDOUT2</td>
<td style="text-align: center;">3</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">11</td>
<td style="text-align: left;">SDIN2</td>
</tr>
<tr class="even">
<td style="text-align: right;">SDOUT3</td>
<td style="text-align: center;">4</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">10</td>
<td style="text-align: left;">SDIN3</td>
</tr>
<tr class="odd">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">5</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">9</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="even">
<td style="text-align: right;">SDOUT4</td>
<td style="text-align: center;">6</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">8</td>
<td style="text-align: left;">SDIN4</td>
</tr>
<tr class="odd">
<td style="text-align: right;">NC</td>
<td style="text-align: center;">7</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">7</td>
<td style="text-align: left;">NC</td>
</tr>
<tr class="even">
<td style="text-align: right;">SDIN4</td>
<td style="text-align: center;">8</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">6</td>
<td style="text-align: left;">SDOUT4</td>
</tr>
<tr class="odd">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">9</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">5</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="even">
<td style="text-align: right;">SDIN3</td>
<td style="text-align: center;">10</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">4</td>
<td style="text-align: left;">SDOUT3</td>
</tr>
<tr class="odd">
<td style="text-align: right;">SDIN2</td>
<td style="text-align: center;">11</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">3</td>
<td style="text-align: left;">SDOUT2</td>
</tr>
<tr class="even">
<td style="text-align: right;">SDIN1</td>
<td style="text-align: center;">12</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">2</td>
<td style="text-align: left;">SDIN1</td>
</tr>
<tr class="odd">
<td style="text-align: right;">+5V In</td>
<td style="text-align: center;">13</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">1</td>
<td style="text-align: left;">+5V</td>
</tr>
<tr class="even">
<td style="text-align: right;">MIDI TX</td>
<td style="text-align: center;">14</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">25</td>
<td style="text-align: left;">MIDI RX</td>
</tr>
<tr class="odd">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">15</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">24</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="even">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">16</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">23</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="odd">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">17</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">22</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="even">
<td style="text-align: right;">FS Out</td>
<td style="text-align: center;">18</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">21</td>
<td style="text-align: left;">FS In</td>
</tr>
<tr class="odd">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">19</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">20</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="even">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">20</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">19</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="odd">
<td style="text-align: right;">FS In</td>
<td style="text-align: center;">21</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">18</td>
<td style="text-align: left;">FS Out</td>
</tr>
<tr class="even">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">22</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">17</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="odd">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">23</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">16</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="even">
<td style="text-align: right;">GND</td>
<td style="text-align: center;">24</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">15</td>
<td style="text-align: left;">GND</td>
</tr>
<tr class="odd">
<td style="text-align: right;">MIDI RX</td>
<td style="text-align: center;">25</td>
<td style="text-align: center;"></td>
<td style="text-align: center;">14</td>
<td style="text-align: left;">MIDI TX</td>
</tr>
</tbody>
</table>
<h2 id="tocanch4" class="tvis">Electrical
characteristics of the interface</h2>
<h3 id="tocanch5" class="tvis">Power</h3>
<p>The +5V supply is derived straight from the +5V rail that goes into
the main board, with polarity protection (both in the XV-5080 and
VS-2400) provided with a Schottky diode, and sometimes a current
protected with a thermistor (not present in the XV-5080).</p>
<p>The +5V pin measured 5.28V to ground on my XV-5080.</p>
<h3 id="tocanch6" class="tvis">Digital Audio</h3>
<p>The format of digital audio portion of R-BUS resembles <a href="https://en.wikipedia.org/wiki/I%C2%B2S">I²S</a>, but with a few
key differences:</p>
<ul>
<li>There’s no bit clock.</li>
<li>Sample data are transmitted as if they are 32-bit, despite only the
first 24-bit is being used.</li>
<li>Logic level on the data line is inverted.</li>
</ul>
<p>To give a standalone description of the R-BUS digital audio
protocol:</p>
<ul>
<li>The frame sync (word clock) signal runs at the same frequency as the
sampling rate.</li>
<li>When frame sync is low, left channel of each channel pair is being
transmitted, otherwise right channel is being transmitted.</li>
<li>Each half cycle of the frame sync clock is divided into 32 periods,
during each of which a bit of sample data is sent on every serial data
line.</li>
<li>Sample data are sent most significant bit (MSB) first. Each sample
is 24-bit long, leaving 8 bits unused at the end of each half cycle of
frame sync.</li>
<li>Logic low on the data line means the bit being sent is 1, and high
means it’s a 0.</li>
</ul>
<p>If you’d like a timing diagram of all this, please look up the
datasheet of TC9271 made by Toshiba (used in the XV-5080 as its S/PDIF
encoder chip). Figure 1b is a good representation of the relationship
between frame sync (LRCK in the datasheet) and audio data. The LRS=H
case in figure 3a shows how the frame sync signal sent over R-BUS should
be interpreted.</p>
<p>There are 4 serial data lines in each direction, giving the 8
channels in total for each direction. Each direction has its own frame
sync signal, which is shared among all data lines in that direction.</p>
<h3 id="tocanch7" class="tvis">MIDI</h3>
<p>What is sent over the MIDI wires in the R-BUS cable has not been
confirmed by me.</p>
<p>The MIDI interface is used differently on different Roland
products:</p>
<ul>
<li>XV-5080 seem to ignore everything on the R-BUS MIDI interface,
despite having all the facilities to handle it. Roland disclosed this in
RPC-1’s user manual (see the section on XV-5080). I have not tested this
claim.</li>
<li>MV-8000 series with MV8-OP1 installed can use the R-BUS MIDI output
as a separate MIDI port. Data going into the R-BUS MIDI port will be
mixed with the built-in MIDI input.</li>
<li>VM-3100Pro can pass through the MIDI data to its built-in MIDI
ports, and can control the host sequencer if connected to a
computer.</li>
<li>V-Studio products can receive MIDI clock over R-BUS.</li>
<li>Any aspects / products not mentioned here are unknown to me.</li>
</ul>
<p>Roland calls the signals that go in to / out of these pins “IPC” or
“PC”. <a id="n9" href="#note9" class="note">[9]</a></p>
<p>Inside both the VS-2400 and the XV-5080, the signal is generated /
goes into a dedicated microcontroller (a M3888 1M2), specifically, a
pair of its UART ports. An inverter is between the R-BUS connector and
the MCU in each direction of the signal.</p>
<p>Roland claims in VS-2480’s manual that R-BUS carries 8 channels of
bidirectional digital audio (which are already fully accounted for in
the previous section), plus MIDI, MMC (MIDI Machine Control) and MTC
(MIDI Timecode).</p>
<p>The factual portion of this section ends here. Everything below is my
guesswork. Since MMC commands and MTC are both usually just sent as
normal MIDI messages, it’s a reasonable assumption that, the only thing
that is transmitted over these wires is MIDI, which is also why I named
them MIDI TX/RX in my pin usage chart.</p>
<p>Since MIDI is pretty much just UART with a bit of isolation, I would
venture a guess that the signal sent / expected on these two pins is
just inverted MIDI UART signal.</p>
<p>It would be pretty trivial to build some experimental circuitry to
test my theory. Maybe I’ll do it one day. However this may end up with
nothing – as the XV-5080 will probably just ignore the MIDI data going
through R-BUS.</p>
</article>
</div><br><hr>
<div class="TText" id="notediv" style="font-size:80%;"><span class="TText"><a id="note1" href="#n1">[1]</a>: Serial data
output (input). Overline indicates that 1-bit is represented with low
logic level and 0-bit with high logic level. Same
below.<br></span><span class="TText"><a id="note2" href="#n2">[2]</a>: Not connected. Same
below.<br></span><span class="TText"><a id="note3" href="#n3">[3]</a>: Inferred from wiring scheme<br></span><span class="TText"><a id="note4" href="#n4">[4]</a>: Often abbreviated
as TX.<br></span><span class="TText"><a id="note5" href="#n5">[5]</a>: Often abbreviated
as RX.<br></span><span class="TText"><a id="note6" href="#n6">[6]</a>: <a href="https://support.roland.com/hc/en-us/articles/201978779-R-BUS-RBUS-RBC-RBC-5-Where-Can-I-Find-an-R-BUS-Cable">R-BUS,
RBUS, RBC, RBC-5: Where Can I Find an R-BUS Cable?</a><br></span><span class="TText"><a id="note7" href="#n7">[7]</a>: <a href="https://web.archive.org/web/20240204170917/https://www.vsplanet.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=450346">Roll
your own: R-Bus Cable Pin Out.</a><br></span><span class="TText"><a id="note8" href="#n8">[8]</a>: <a href="https://web.archive.org/web/20211204221550/https://themidimaniac.com/diy-r-bus-cable-for-20e/">DIY
R-BUS cable for 20€</a><br></span><span class="TText"><a id="note9" href="#n9">[9]</a>: I have no idea what these could mean. My
software-dominated brain tells me they stand for “Inter-Process
Communication” and “Program Counter” but they clearly stand for
something else here.<br></span></div>
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