new SBUS info in camera user manual

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Stu Aitken

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new SBUS info in camera user manual

PostMon Nov 20, 2017 3:53 am

the updated info on how the camera communicates via sbus in the manual update that comes with 4.7 firmware is welcome but I have a question:

it talks about suitable values as if the channels held 8 bit values - ie 0-255 with a 'median' value of 123

however sbus channels are 11 bit (0-2047, with the median value therefore sitting at 1023) and in my previous tests with an arduino connected to the camera, that certainly seemed to be the case (ie the camera uses 11 bit values as expected)

am I missing something here or is the uses of 8 bit values in the examples in the manual an error?
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Kristian Lam

Blackmagic Design

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Re: new SBUS info in camera user manual

PostTue Nov 21, 2017 4:31 am

Hi Stu,

While S.Bus does use 11-bit values, we only care about the 8 most significant bits.
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Stu Aitken

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Re: new SBUS info in camera user manual

PostWed Nov 22, 2017 8:49 pm

Kristian Lam wrote:Hi Stu,

While S.Bus does use 11-bit values, we only care about the 8 most significant bits.


thanks for that Kristian

but - I think this is important - that still means sending an 11 bit value (ie 1023 as opposed to 123) to the camera from the controlling device

even if its truncating the values back down to an 8 bit range, you still need to essentially give it the bigger number to start with

I appreciate that if you might be setting bit values directly this maybe seems trivial but it still seems to me that its very open to people misinterpreting that information, if they are likely to be coding using decimal integers

eg:

0123 decimal is 00001111011 (11 bit binary) - losing the 3 least significant bits = 00001111
1023 decimal is 01111111111 (11 bit binary) - losing the 3 least significant bits = 01111111

BIG difference :)

its a shame it doesn't use all the precision though practically this maybe only affects the theoretical granularity of the focus adjustments possible

does this mean that PWM is arguably better than SBUS on that basis? or is the PWM signal being sampled to 8 bit as well?

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