16bit over midi LSB/MSB

[fubbi]

Hello

I am working with a MIDI to SERVO controller and need some help understanding the concept of MSB/LSB and 16bit math

This controller can take a coarse and a fine value broadcast over 2 MIDI channels. The only information I can find is pertaining to DMX. 

I am unsure how this scales to MIDI. I need 0-127 and I am wondering if I should just swap 256 for 127 in the code below, or does that mess up the math?

Thanks for any advice!

Fubbi

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Here is what I know so far:

In order to make a "high res" input in Isadora I have come to the following conclusions by studying the coarse/fine behavior of DMX fixture control:

• Coarse is the MSB (Most Significant Bit) and Fine is the LSB (Least Significant Bit)

• 16 bit is equal to 65535

• For DMX the LSB is input % 256 (modulo)

• For DMX the MSB is floor(input/256)

I concocted the following javascript to scale and split a 16bit value to LSB/MSB

// iz_output 1 "LSB"

// iz_output 2 "MSB"

function main()

{

var input = arguments[0];   // input 1 [0-65535]

    var n = Math.trunc(input); // float to integer, maybe redundant

var LSB = n % 256; // for dmx this is how LSB is calculated

var MSB = Math.floor(n/256);  // for dmx this is how MSB is calculated

return [LSB, MSB]

}

[fubbi]

Update:

Actually, it's supposed to be 14 bit (16384?) for midi, so now I am really curious if I am on the right track

Since each controller message has only a 7-bit value field, many MIDI devices utilize some controllers in pairs to achieve a full 14-bit resolution. These can be thought of as the “coarse” adjustment for the most significant 7-bits (MSB), and the “fine” adjustment for the least significant 7-bits (LSB). 

[Juriaan]

@fubbi

If the code of DMX is the following (and you know this is correct)

// iz_output 1 "LSB"

// iz_output 2 "MSB"

function main()

{

var input = arguments[0];   // input 1 [0-65535]

    var n = Math.trunc(input); // float to integer, maybe redundant

var LSB = n % 256; // for dmx this is how LSB is calculated

var MSB = Math.floor(n/256);  // for dmx this is how MSB is calculated

return [LSB, MSB]

}

DMX is 512 channels, 256 is exactly .5 of 512. So I would personally think that if it expects 14 Bit MIDI that we should divide by 0.5 * 16384 = 8192

[fubbi]

@juriaan said:

DMX is 512 channels, 256 is exactly .5 of 512. So I would personally think that if it expects 14 Bit MIDI that we should divide by 0.5 * 16384 = 8192

 Hi Jurian, thanks for jumping in. But divide where? I am not sure what you mean. The size of the incoming number could be relatively arbitrary as the servos will just stop moving outside their scope. I changed my script from 256 to 127 and I get pretty consistent movement from 0 to 16384.

Now if it really makes the movement so much more high res is another question. I have come to believe that it really only matters if you need to make very precisely positioned stops.

Cheers