Absolute Encoder Questions / SSI via 5i25

juwi
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23 Oct 2012 20:32 #25705 by juwi

Replied by juwi on topic Re:Absolute Encoder Questions / SSI via 5i25

PCW wrote:

[...]

If you want me to make a config with the free SSERIAL port on a 7I77 used for SSI just ask

Hereby asking - Lascar says 3 weeks delivery time for the 7i74

Thank you!

Regarding the rest of your mail, that makes more sense than a grey pin and a binary pin per SSI. Thanks for your suggestions!

best regards,
julian

compiling emc......

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PCW
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23 Oct 2012 21:02 #25707 by PCW

Replied by PCW on topic Re:Absolute Encoder Questions / SSI via 5i25

freeby.mesanet.com/7i77_ssi_7i74.bit

Has just one SSI interface on the 7I77s RS422/485 expansion port
Note that this expansion port is a RS-485 capable interface so has a /XMIT
enable on GPIO-0 you will need to set low by making GPIO-0 an output and setp-ing it low
in your hal file

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andypugh
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23 Oct 2012 21:26 #25711 by andypugh

Replied by andypugh on topic Re:Absolute Encoder Questions / SSI via 5i25

PCW wrote:

GrayCode (bit) binary if false, graycode if true

Why would you use Gray code on a serial protocol?

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juwi
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23 Oct 2012 21:29 #25712 by juwi

Replied by juwi on topic Re:Absolute Encoder Questions / SSI via 5i25

andypugh wrote:

PCW wrote:
GrayCode (bit) binary if false, graycode if true

Why would you use Gray code on a serial protocol?

SSI is either grey or binary coded...

Ist SSI specific.

Best regards,
Julian

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andypugh
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23 Oct 2012 21:32 #25713 by andypugh

Replied by andypugh on topic Re:Absolute Encoder Questions / SSI via 5i25

juwi wrote:

[SSI is either grey or binary coded...

Yes, I understand that. I am wondering why.

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juwi
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23 Oct 2012 21:36 #25714 by juwi

Replied by juwi on topic Re:Absolute Encoder Questions / SSI via 5i25

Probably historical reasons... Grey Code has been used on rotary encoders...
SSI is just a shift register, easy to integrate. So you stay where you are with what you have and extend it?

Beste regards,
Julian

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PCW
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23 Oct 2012 21:38 #25715 by PCW

Replied by PCW on topic Re:Absolute Encoder Questions / SSI via 5i25

Historically absolute encoders (brushed or optical) were parallel interfaced
so always used gray codes to prevent large errors at transitions
probably most early SSI encoders used simple logic circuits to
serialize the parallel gray code data. Converting to binary at the
encoder is a newer innovation.

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juwi
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23 Oct 2012 21:42 #25716 by juwi

Replied by juwi on topic Re:Absolute Encoder Questions / SSI via 5i25

I am typing on my mobile and have been faster ;-)

Good night :-)

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juwi
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08 Nov 2012 00:18 #26347 by juwi

Replied by juwi on topic Absolute Encoder Questions / SSI via 5i25

Ok, after looking a bit deeper into this, I have some additional Things to do...

Questions:

- What Signals are really needed? velocity, position, ?
- Velocity can be calculated as in encoder.c?

best regards,
Julian

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PCW
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08 Nov 2012 01:04 #26348 by PCW

Replied by PCW on topic Absolute Encoder Questions / SSI via 5i25

With SSI you are stuck with calculating velocity as delta-position/delta-time

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