bearcat wrote:1 - Decided to buffer all except TDI for the JTAG?
I merely follow-up on the XK1 design which sorts of make sense: buffer out the TDO and put some schmidt triggers on the clock-like inputs.
bearcat wrote:2 - The XLINK's are very high speed. I would wonder if some R33's on those lines is prudent since they go off board.
Yes, I know this is the recommendation for lengths of around 10cm. Since I only have 4cm with my board connectors, I thought I could avoid those. I suppose that I would lower the clock if I had some issues with the links.
bearcat wrote:3 - No connection of the USB shield via cap to ground? Or did I miss that in the schematics.
I have never done that on any of my design...
bearcat wrote:4 - I believe there is a 1K from Vbus to the USB3318 in the reference designs (I don't have the schematics handy to verify). Don't have the datasheet for that part so can't see what the manufacuture recommends or why it's there. No cap on Vbus line for the USB3318? Is the combination of R and uF's form a low pass filter for the USB3318?
I will check this. I sort of followed up on the design of the XTAG, assuming that XMOS had done their homework on a key piece of their development chain!
bearcat wrote:5 - Having a max of 5.5V for power In with no protection seems risky. Lots of unregulated supplies that say 5V but may actually be much higher and a user not knowing the difference. Maybe this is typical with Arduino systems??? It would make me nervous.
Yes, you are right. I guess I am using in most cases USB as a power, so no problem.
I will have a look again at alternative regulators with wider input ranges. The one selected has a good price though and absolute max of 7V. Reading the data sheet, I just realized that the minimum voltage for input is 4.5V, so not too good for battery input. So another candidate is the LM2734 which is just twice as expensive...