Handbook for the SX Midi Filter Wheel - Issue 1, January 2019
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Starlight Xpress Midi Filter Wheel
Communication Protocols
Interfaces available:
USB: 1.1 or 2.0
General parameters:
Total Filters:
This is the number of filters fitted on the wheel, and is 7 for the
standard Midi Wheel.
Filter number:
This is any number from 1 to <Total Filters>
(If a Filter Number higher than Total Filters is requested then the Filter
Number is set to <Total Filters>)
USB Protocol:
The SX filter wheel uses a simple “Human Interface Device” protocol, so no
special driver needs to be installed. The driver is an integral part of the
Windows PC operating system.
Communications between the PC & filter wheel is by input and output
reports (referenced to the PC). These reports are both of a fixed length of
two bytes. The PC sends the output report and the filter wheel, about 1ms
later, will send an input report in response.
The output report data is formatted thus:
Description
1
st
byte
2
nd
byte
Select Filter
New Filter number
Zero (0)
Request current filter number
Zero
Zero
Get Filter Total
Zero
One (1)
The input report data is formatted thus:
Response To:
1
st
byte
2
nd
byte
Select New Filter
New Filter number
or
Zero = filters moving
Total filters
Request current filter number
Current Filter number
or
Zero = filters moving
Total filters
Get Filter Total
Current Filter number
or
Zero = filters moving
Zero
NB: The ‘Get Filter Total’ command responds straight away with a “filters
moving” message. However, there is a delay of several seconds before the
Total Filters data is available to the “Request Current Filter Number”
command. This is the time taken for the wheel to complete between one and
