Synthesis Technology MOTM-650 User manual

MOTM-650 4 Channel
MIDICV Converter
User’s Guide
Firmware Version 1.4
Synthesis Technology
6625 Quail Ridge Dr.
Fort Worth, TX 76180
[phone]
www.synthtech.com
October, 2011

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GENERAL INFORMATION
Thank you for purchasing the MOTM-650 4CH MIDI-CV Converter. If you have any issues
concerning the use of the MOTM-650, please contact us at (888) 818-MOTM or by email:
[email protected]
TROUBLESHOOTING GUIDE
If your MOTM-650 does not work as expected, keep in mind the MOTM-650 is a complex
modal device, and more often than not, problems encountered are related to a higher level
feature set to an unexpected value.
THEORY OF OPERATION
The MOTM-650’s functionality is provided by an Atmel AT89C51RD2 embedded CPU, a
version of the 8051. Its built-in UART is used to send and receive MIDI data, and its
internal clock is used to drive the 650’s two arpeggiators. Its internal FLASH memory
makes it possible to update the chip’s firmware via MIDI. The chip has numerous inputs
and outputs which are used to read the front panel buttons and the clock input, to control
the LCD, and to drive the gate outputs & LEDs. The CPU also has an SPI interface which
is used to talk to the two analog-to-digital converters (ADCs).
The four main CV outputs are provided by an AD5541 16-bit ADC. Its output is fed into a
DG408 4-channel analog demultiplexer, which provides four control voltage (CV) outputs
from the in turn feeds four AD822 dual op-amps. The AD822s sample and hold the CVs
between updates from the CPU, which occur once every millisecond.
The eight velocity and auxiliary CV outputs are provided by a TLV5608 8-channel 10-bit
ADC. Because this chip has eight latching DACs, it does not require a demultiplexer or
sample-and-hold circuitry. Its outputs are buffered by two TL074 quad op-amps.
TERMINOLOGY AND SYMBOLS
Settings are module features which can be changed using the MOTM-650’s front panel user
interface or via MIDI System Exclusive (SysEx) or Continuous Controller (CC) messages.
Options are the various choices that can be made for each setting.
Voices are the 4 vertical groups of CV, GATE, VEL, & AUX output jacks, which are usually
associated with one of the current MIDI Note On messages.
BOLD fonts like this in the middle of text indicate a button, jack, or LED legend on the
MOTM-650’s front panel.
Bold fonts like this indicate the name of a Setting or Option.
Fonts like this show what appears on the MOTM-650’s LCD.

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FRONT PANEL
The MOTM-650’s front panel looks like this:

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From top to bottom:
LCD – This 8 character by 2 line LCD is the primary user interface for settings, status, and
other MOTM-650 related information. The LCD backlight can be controlled via global
settings.
MIDI – Indicates MIDI activity on input to the MOTM-650. This is an indicator of all MIDI
data sent to the MOTM-650’s MIDI IN – not just MIDI data bound for the MOTM-650. Note
that this LED is lit by the MOTM-650’s processor, not directly from MIDI data pin.
V1-V4 LEDs – These LEDs indicate when a voice’s gate is either on (lit) or off (not lit). If a
voice is set as an S Trigger, an LED on indicates the gate is shorted and off indicates the
gate is open.
BEAT LED – This LED will blink at the rate of the clock source.
ESC – The ESCAPE button is used to either cancel a setting change, or move to a higher
level function. Just remember, when in doubt, press ESC.
ENTER – The ENTER button is used to accept a setting change, step to a lower level
function, or confirm that a changed setting is desired.
DEC / INC – The DECREMENT and INCREMENT buttons are used to step through the
menu options and change settings. In some contexts, holding down either button will cause
an accelerated repeat of either button, which makes changes happen more quickly (much
like the key repeat on a computer keyboard).
MIDI IN – The MOTM-650’s MIDI input.
MIDI OUT – The MOTM-650’s MIDI output.
EXT CLK – External clock pulse input for external clocking of the MOTM-650.
AUX 1-4 – 10 Bit assignable auxiliary outputs – one for each voice. Each output has its own
settings and menus to control them. See the Voice Group Settings section of this manual
for information on their operation.
VEL 1-4 – 10 Bit velocity output or trigger output. The function of these jacks is dependent
on their Voice Group Setting.
GATE 1-4 – Gates for each of the individual voices. These directly track the Voice 1-4 LEDs
as described above.
CV 1-4 – 16 Bit control voltage outputs, used to convert MIDI note data to control voltages.
They are usually connected directly to VCOs, but can be used for any module that needs a
highly accurate control voltage.

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USER INTERFACE INTRODUCTION
Before getting in to the specifics of the MOTM-650’s feature set, let’s get comfortable using
the MOTM-650’s user interface. Switch on the MOTM-650. The LCD will light up and
indicate the MOTM-650 and its firmware version number, followed by a screen looking
something like this:
G1 CH=1
Solo
For now, ignore its meaning – press ENTER. The MOTM-650 will display this:
Global
Settings
Press the DEC / INC buttons to scroll through the top-level user functions. INC moves
forward and DEC moves backward through the list of top-level functions. Notice that
eventually the options will loop back around to Global Settings.
With INC or DEC, select Global Settings and press ENTER. The LCD will show:
VGrpType
4
Get comfortable scrolling through the Global Settings by using INC or DEC, and when
finished, press ESC. This backs the display out to the top-level menu, and will show:
Global
Settings
This is how the entire menu system is structured – a top level of function categories,
followed by a single level of settings or actions. And pressing ESC at any time will back up
one level.
Okay, now that you have a basic understanding of top-level/sub-level menus, get the screen
back to Global Settings, and press ENTER to display the first setting, VGrpType. For the
time being, let’s ignore what this means, and use the INC or DEC buttons until the display
shows:
Clock
Internal
The display will be steady. Press ENTER – notice that Internal begins to flash. This
indicates that the setting can be changed. Press INC or DEC to scroll through INTERNAL,

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MIDI Clk, Ext. Reg, or Ext. Irr. Select MIDI CLK, and press ENTER. The display should
show:
Clock
MID IClk
…and MIDI Clk should be steady. You’ve just changed the clock source from the 650’s
internal clock to MIDI clock. This is how any setting is changed – press ENTER to edit the
setting, use INC or DEC to choose an option or set the value, and press ENTER again to tell
the MOTM-650 to store the change.
Let’s try one more aspect of the MOTM-650’s user interface – With the display showing
Clock MIDI Clk, press ENTER again. MIDI Clk will begin to flash. Use INC or DEC to
select Internal on the display, but instead of pressing ENTER, press ESC instead. The
display will show:
Clock
MID IClk
This allows the user to back out of a change before it becomes permanent, and the setting
will be set back to whatever it was before the change was made.
In short, press ENTER to edit a setting, change the setting with INC or DEC, then press
either ENTER to select the change or ESC to cancel it. All the settings work this way!
Keep in mind that the entire MOTM-650’s user interface works just as above, regardless of
function or feature.
Note that all MOTM-650 setting changes can be transmitted via MIDI. This is useful when
a live performance is being done and a recording of all front panel changes is desired.
All settings are stored in internal flash memory. Once a setting change is made, it’s saved
across power cycles. The MOTM-650’s entire active state is saved in nonvolatile memory.

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DETAILED FEATURE DESCRIPTION
Top-level Function Categories
The MOTM-650’s functionality can be broken up into four categories:
Global Settings – Global settings apply to the MOTM-650 as a whole. Most global settings
apply to all voice groups simultaneously. These features include, but are not limited to,
clock source, tuning tables, tempo, voice group configuration, etc…
Voice Group Settings – A voice group is a logical grouping of voices that share the same
settings, including MIDI channel.
Arpeggiator Settings – The MOTM-650 has two arpeggiators, each of which can be
assigned to a voice group, no voice group, or both to the same voice group. Arpeggiators use
settings from global settings (such as clocking) and have their own settings available.
Module Actions – These are one-shot actions that perform various functions, such as
dumping patches, storing patches, etc… They are not settings as in global, voice group, or
arpeggiator categories, rather just instructions to perform a specific action.
Note: Settings may appear and disappear in the menus depending upon how the MOTM-
650’s options are set. For example, setting the Clock Source to MIDI Clock will cause the
Internal Clock BPM setting to disappear from the Global Settings menu. There are only
a few cases where this occurs, and it’s done to ensure that only the settings that will have
an effect on the MOTM-650’s operation are visible at any given time. If one of the expected
setting doesn’t appear, check the MOTM-650 Menu Chart in Appendix A to see if another
setting controls whether or not it appears.
Global Settings
The MOTM-650 has the following settings with a global effect:
Voice Group Type
Velocity Scale
Trigger Pulse Width
Solo Note Priority
Tuning Table
Note Inversion
Backlight Intensity
System Status
SysEx Device ID
Global Control MIDI Channel
Patch Reception
Clock Source
MIDI Clock Output
Internal Clock BPM

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Return to the menu’s top-level by pressing ESC a couple of times, then press INC until the
LCD displays:
Global
Settings
Press ENTER, and the first setting will be displayed – the Voice Group Type (abbreviated
as VGrpType).
Note::In reviewing the settings and their associated options, each setting will be presented
in the center of the page abbreviated as it appears on the LCD, along with its default option.
The full name and description of the setting will follow, and then each option or group of
options will be explained.
VGrpType
4
The Voice Group Type setting sets the number and configuration of voice groups
available. At this point, you may be wondering – what is a voice group? A voice group is a
logical grouping of the MOTM-650’s four voices, allowing each voice to either share control
settings or have separate settings, depending on how the voices are being used. For
example, if you have several VCOs and want to use them polyphonically, you’ll probably
want to group them together so they have the same settings. If, on the other hand, you’re
using your MOTM-650 to control four monophonic synth voices, it may make sense to have
different settings for each voice. The Voice Group Type setting allows the following
combinations of voice groups:
4- 1 Voice Group with all 4 voices.
2/2 - 2 Voice Groups with 2 voices per group
1/1/1/1 - 4 Voice Groups with 1 voice per group
You will probably only change the Voice Group Type when setting up a new patch, as it
radically changes the way that MIDI data is interpreted and routed to the MOTM-650’s 16
CV outputs.
For now, leave the Voice Group Type set to 4. The settings available to each voice group
will be explained later.

VelScale
_4Volts
The Velocity Scale setting sets the output scaling of the VEL outputs when they are set to
output velocity. It can be set to output 1, 2, 4, or 8Volts when a velocity of 127 is received,
and will be scaled between 0 volts and full scale in proportion to other velocity values.
Trig PW
10ms
The Pulse Width setting sets the width in milliseconds of the GATE outputs when they are
set to Shorting Trigger mode, and the VEL outputs when they are set to Trigger mode.
The width can be set to 1, 10, or 100 ms, with an accuracy of 2 ms.
Priority
LastNote
The Solo Note Priority setting controls which note is voiced when the Voice Allocation
Mode is set to one of the solo modes and several notes are held.
LastNote
Last Note priority uses the solo voice(s) to sound the last note played. Last note is how
most monosynths operate.
Low Note
Low Note voices the lowest note still held. This is useful for playing the low note of a
chord to double the bassline.
HighNote
High Note voices the highest note still held. This is best used for playing a solo using the
high note of a chord.

TunTable
__12 Tone_
The Tuning Table setting sets the tuning table used to map the MIDI note values to the
CV output voltages. There are 16 tuning memories to choose from. These are programmed
at the factory with 16 tunings, which were selected by Robert Rich (see Appendix B for
Robert’s description of each tuning). All but the first Tuning Table (standard Equal
Temperament) can be overwritten by sending MIDI Tuning Standard messages to the
MOTM-650. Once overwritten, they can only be restored by sending the 650 a tuning dump
with the correct tuning data.
The default tunings are as follows:
Name Memory Description
12 Tone 1 12 Tone Equal Temperament
HrmA1 -60 2 Harmonic Series
HrmA1 -12T 3 Carlos Harmonic 12 Tone
Meantone 4Meantone Temperament
1/4TonET 5 ¼ Tone Equal Temperament
19TonET 6 19 Tone Equal Temperament
31TonET 7 31 Tone Equal Temperament
PythagoC 8 Pythagorean C
JIA7/5D# 9 Just Intonation in A w/ 7-limit Tritone at D#
3 -5LattA 10 3-5 Lattice in A
3 -7LattA 11 3-7 Lattice in A
7LimBlkC 12 Other Music 7-limit Black Keys in C
PelSlenB 13 Dan Schmidt Pelog/Slendro
JIMajYam 14 Yamaha Just Intonation Major C
JIMinYam 15 Yamaha Just Intonation Minor C
Partch11 16 Harry Partch 11-Limit 43 Note Just Intonation
Note Inv
_Off
The Note Inversion setting turns note inversion On or Off.