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TP: Data transfer between lens and body.
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Dorset Mike View Drop Down
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Posts: 535 		Post Options Post Options   Quote Dorset Mike Quote  Post ReplyReply Direct Link To This Post Topic: TP: Data transfer between lens and body.
    Posted: 25 May 2007 at 15:09
Can anyone tell me (or direct me to a web site) how data is transferred between a lens and the camera body? Is it say some of the pins define the lens focal length others define aperture, or is it more complex like serial or parallel data transmission where the body reads successive locations within the lens chip.
I would suspect the latter as 5 pins on the older lenses could only have given a maximum of 32 conditions if it relied on static binary levels, whereas accessing locations within the chip gives far more.
Cheers MIKE
Cheers MIKE,



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nigelbrooks View Drop Down
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Posts: 8520 		Post Options Post Options   Quote nigelbrooks Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2007 at 16:49
Afternoon Mike.

For the hell of me I can't find the site (I think it was Russian) but I do recall mention of "31 data elements", which would almost tie-in with static binary over five pins, being read from the lens when the ROM was 'interrogated'.

If I find the page I will post a link to it here.

EDIT: OK the site was Malaysian not Russian -oops! and here's the link.

Edited by nigelbrooks - 25 May 2007 at 16:53
Away until August 2014 at the earliest.
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analytical View Drop Down
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Posts: 3069 		Post Options Post Options   Quote analytical Quote  Post ReplyReply Direct Link To This Post Posted: 25 May 2007 at 21:08
Originally posted by Dorset Mike Dorset Mike wrote:

Can anyone tell me (or direct me to a web site) how data is transferred between a lens and the camera body? Is it say some of the pins define the lens focal length others define aperture, or is it more complex like serial or parallel data transmission where the body reads successive locations within the lens chip.
I would suspect the latter as 5 pins on the older lenses could only have given a maximum of 32 conditions if it relied on static binary levels, whereas accessing locations within the chip gives far more.
Cheers MIKE


If one pin is power and another ground, then that's only three data pins, and 8 static states.   
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Pete Ganzel View Drop Down
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Posts: 941 		Post Options Post Options   Quote Pete Ganzel Quote  Post ReplyReply Direct Link To This Post Posted: 26 May 2007 at 02:00
Hi Mike:

A lot of work has been done by folks who post here.

See postings by vasimv like this;


Focus Confirmation
Several useful things have come of this such as focus confirmation with non AF lenses.

What I have found is that the protocol is serial, (specifically, SPI).

Here is a pinout of the Minolta AF lens connector.




The data stream is over a single wire, two if you count Gnd.


All of the lens focus and focal length encoders I've looked at are four or five bit binary, the lens chip translates that into serial data.

Pete



Edited by Pete Ganzel - 26 May 2007 at 02:03
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