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What's inside a KeySpan serial adapter?

cheesestraws

Well-known member
A very quick post: I recently acquired a couple of KeySpan serial adapters from @pcamen: one for use and one to take to bits for science, in case it wouldn't go back together.  In fact, the whole thing comes apart and goes back together very cleanly; there's just one screw, under the label:

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And the whole thing lifts out as one circuit board.  The strain relief slots into the case, it isn't glued in, so it's easy to get out and in.

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What have we here?

First of all, we'll have no luck trying to get this to talk LocalTalk; each port is being looked after by an OX16C950, which is a UART.  It does not have synchronous serial, and it does not support SDLC.

IMG_1590.JPG

However, it does claim to have RS485 support, and the line drivers are 75LBC776s, which are full geoport transceivers.  Those, plus the inverter between the two, do suggest that differential signalling is probably in place here.

IMG_1590 2.JPG

The remaining major chip, unsurprisingly, is an USB interface/microprocessor type affair, part of the communicatively-named "EZ-USB" series.  This loads its firmware over USB from the host (!), so in theory this is hackable (though why would you?  There are easier ways of getting a custom USB-attached UART).

That's really all there is.  When putting the adapter back together, note that the shielding on the USB cable needs to pop into the little copper clip.  When I took it to bits this popped out and needed replacing.

RenderedImage.jpg

So, in summary:

  • Will do fast asynchronous serial, including in theory with an external clock.
  • Will probably do differential signalling.
  • Will not do synchronous serial, and definitely not SDLC, so no LocalTalk.



Hope this is useful to someone.

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IMG_1590.JPG

 

Trash80toHP_Mini

NIGHT STALKER
Great workup! Does it require drivers? Are all the ICs off the shelf or have programmable features/complicationss? PCB has how many layers?

 

cheesestraws

Well-known member
Does it require drivers?


Yes, it will do; the EZ-USB controllers, according to their datasheet anyway, download their firmware from the host.  So this requires specific drivers that contain the relevant firmware.

Are all the ICs off the shelf or have programmable features/complicationss?


The only IC I couldn't find a datasheet for was the geoport line drivers, but those realistically aren't going to be black magic.  The UARTs and USB controller are discontinued but from lines that still have scions.

PCB has how many layers?


Didn't occur to me to look—sorry!

 

AndiS

Well-known member
Interesting.  What (bundled) driver does it use?


Good that you asked - it is not as I remembered. It does work but you need the firmware files too!

You can enable these specific Keyspan adapters very deep down in the Kernel config if you build your own Kernel. But since the Linux Distribution usually configure everything and the kitchen sink, this is not a problem.

I have set it up in the past and I just remember how easy it was back then. So I forgot about the firmware which is not included in a standard Debian install. This is true for a lot of things though, I just have to figure out in which firmware package the files hide ;-)

Will report tomorrow.

 

cheesestraws

Well-known member
I have set it up in the past and I just remember how easy it was back then. So I forgot about the firmware which is not included in a standard Debian install. This is true for a lot of things though, I just have to figure out in which firmware package the files hide ;-)


Ahhhh yes, that makes more sense.  I was wondering if I'd misread the controller's datasheet, is all—or, indeed, whether someone had been keen enough on these to write their own free firmware for it!

 

AndiS

Well-known member
While looking for the Linux firmware files I found this:

Hacking the Keyspan USB Serial Adaptor

Relevant and interesting!

I'm still looking for the firmware files. I'm pretty sure they used to hide somewhere in the "nonfree" firmware packages of Debian - just seem to have vanished though ;-)

 

AndiS

Well-known member
Knew it - just when I found the missing firmware files on the internet, I remembered where I saved the according archive a few years back.

So with the firmware files it just works. The Serial ports are /dev/ttyUSB0 and /dev/ttyUSB1 - easy ;-)

 

cheesestraws

Well-known member
Relevant and interesting!


Interesting twice!  I didn't realise the translucent ones were different inside to the opaque ones.  I'll obviously have to take my opaque one apart as well.  The transparent one definitely, as that site says, uses discrete UARTs rather than an integrated UART on the controller.

 
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