Galvanic isolation of SWD lines ?

[lpcware]

Content originally posted in LPCWare by ArneB on Fri Jul 29 02:37:21 MST 2011
In my next project I have to isolate the serial wire debug interface of my LPC1114, because I power my board from a different power domain than my LPC Link.
My problem is the bidirectional SWD line. I have found so far only isolators designed for I2C with a bidirectional port (e.g. ADUM1250), but they are too slow (max. 1 MHz). As far as i understood, the debug port uses higher clock frequencies (4..8 MHz ?)

Does anyone have any recommendations or maybe already schematics how to do it ?
Thank you for your help :)

[lpcware]

Content originally posted in LPCWare by NXP_Europe on Sat Jul 30 11:27:54 MST 2011
Hello ArneB,

other possible solution is to reduce the speed ...

see: http://support.code-red-tech.com/CodeRedWiki/MultipleJtagDevices?highlight=%28speed%29%7C%28swd%29

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Quote:

[B]Reducing wire [B]speed[/B][/B]


When connecting to a remote target , the Code Red IDE will determine what it believes is a safe [B]speed[/B] to obtain stable communication at. The tools use a built in maximum value to start this "negotiation". The default frequencies are typically 3 MHz (CM0/CM3/CM4), 1 MHz (ARM9), and 250 KHz (ARM7) - though this may change between releases.
However these values can be tweaked by the user, as depending on their system it may be necessary to reduce the maximum [B]speed[/B]. This is particularly the case when communicating over JTAG with multiple devices on the scan chain.
To do this, you can change the "Maximum wire [B]speed[/B]" setting in the launch configuration(s) for a particular project from "default" to specific value (accessible via the debugger tab of Launch Configurations -> Open Current Launch Configuration).
Typically we would recommend starting with a low value (eg 250 KHz), and increasing this until you reach a point where communication with the target becomes unreliable. [B]Note :[/B] This above wire [B]speed[/B] information only relates to connections using RedProbe(+). LPC-Link only supports fixed wire [B]speed[/B]s.

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[lpcware]

Content originally posted in LPCWare by TommyBurger on Fri Jul 29 09:10:51 MST 2011
An alternative solutions is to isolate the lpc link from the PC. There are off the shelf USB isolators for about $100 US.

[lpcware]

Content originally posted in LPCWare by ArneB on Fri Jul 29 05:06:10 MST 2011
Hi Zero,

yes, I know this little (fast delivery, but expensive) shop... :D

There is only a small drawback, which I forgot to mention in my first post: The only available voltage on my target board is 2.5V. The minimum recommended voltage of the Avago optocoupler is 3.0V...
I have only a few mA on my board available, therefore i can't use a step-up regulator or something similar...

Seems that i have found a little brain teaser for the weekend... :cool:

BTW, here is an interesting application note from TI concerning this topic:
http://focus.ti.com/lit/an/slyt403/slyt403.pdf

[lpcware]

Content originally posted in LPCWare by Ex-Zero on Fri Jul 29 03:32:27 MST 2011
You can buy something faster (15MBd) in a little shop called 'Farnell' :eek:

http://de.farnell.com/avago-technologies/acsl-6210-00re/optokoppler-smd-zweifach-bi-dir/dp/9130144

AN with schematic:

http://www.farnell.com/datasheets/312935.pdf