sparkfun txb0104 level sifter and nrf52

RE: sparkfun txb0104 level sifter and nrf52

bjorn-spockeli — Fri, 15 Jul 2016 13:56:43 GMT

Glad to hear you got it to work!

RE: sparkfun txb0104 level sifter and nrf52

Matts — Fri, 15 Jul 2016 12:45:51 GMT

There is and was problem with the grounding. The ground level is now better, but still there's some distortion, but signal goes through.

Thanks for the support!

RE: sparkfun txb0104 level sifter and nrf52

bjorn-spockeli — Fri, 15 Jul 2016 12:29:20 GMT

The default MISO drive strength is standard, i.e. (Min. 1mA Typ. 2mA Max. 4mA) so it should be ok, see this infocenter page for the electrical specifications. However, you could try to configure the MISO pin to high drive, (Min. 6mA Typ. 9mA Max. 14mA), see this page.

Lastly, this might be a stupid question, but youre sure that the level shifter is properly grounded?

RE: sparkfun txb0104 level sifter and nrf52

Matts — Fri, 15 Jul 2016 11:28:40 GMT

I think the problem is the master or level sifter here. I measured the loose connector again (so just nrf side signal), and I saw nice looking square wave response on miso. However with the level sifter attached the signal clearly doesn't pull it low enough. The signal was OK, but it didn't go low enough. The master line is miso, so I don't think that's the issue, but could it be that the nrf doesn't have enough pull to actually drive the chip correctly? I mean this is level sifter is meant for SPI.

TI spec says +-2mA is required for driving the cirquit.

RE: sparkfun txb0104 level sifter and nrf52

Matts — Fri, 15 Jul 2016 10:42:30 GMT

And just to elaborate. The first one is clock + miso and second is clock+mosi.

RE: sparkfun txb0104 level sifter and nrf52

Matts — Fri, 15 Jul 2016 10:30:55 GMT

Both are from nrf side. The other side is pretty much the same, except the logic level. Also it doesn't matter if we've connected the level sifter to MISO at all. The output directly from nrf side pin is similar.

I've tried the code itself on another master with those different pins, and it outputs the stuff OK to bus. Dunno if the problem here is too much load on other channels or something. As I said, if I connect another level sifter to VDD the USB stops working.

RE: sparkfun txb0104 level sifter and nrf52

bjorn-spockeli — Fri, 15 Jul 2016 10:25:25 GMT

The first picture is from the nRF side and the second is the output from the level shifter?

RE: sparkfun txb0104 level sifter and nrf52

Matts — Fri, 15 Jul 2016 09:30:04 GMT

The miso still sucks. See attached picture in the question.

RE: sparkfun txb0104 level sifter and nrf52

Matts — Fri, 15 Jul 2016 09:20:25 GMT

We had the spi lines connected to different IO pins than in your example. I was using 11-14 due shorter connection in our mount. I swithed to pins you guys are using in SPIS example and the signals were OK.

Interestingly if I connect two of these components using two different VDD outs from the nrf52, USB stops working.

RE: sparkfun txb0104 level sifter and nrf52

bjorn-spockeli — Fri, 15 Jul 2016 09:09:38 GMT

SPI peripheral on the nRF52 is activly driven, i.e. Push-Pull, so this should not be an issue. Are you able to provide a logic trace/capture of the SPI lines? If so could you provide a trace of the SPI input and output to/from the level shifter.

I also found this in the comment section on the Sparkfun product page(here is the link) :

One problem I ran into–and it is a problem with the IC, not with SparkFun’s breakout board–is that the IC will oscillate if the load on any output is too heavy. If you find that is the case, add a buffer IC downstream of the output.

-Bjørn