nRF52832 SPI 4-Wire Master Issue with SPI Sample

RE: nRF52832 SPI 4-Wire Master Issue with SPI Sample

Mark J — Wed, 10 Aug 2016 13:43:20 GMT

Yes. Issue was with measurement and not actual signals.

RE: nRF52832 SPI 4-Wire Master Issue with SPI Sample

bjorn-spockeli — Wed, 10 Aug 2016 11:14:57 GMT

@mjanke : Have you been able to resolve the issue?

RE: nRF52832 SPI 4-Wire Master Issue with SPI Sample

Mark J — Fri, 15 Jul 2016 00:09:59 GMT

Thanks Daniel. The reception of the leading 0xFF is clear to me now. The strange scope signals remain a mystery and are most likely just an issue with the scope or my setup of it (I am a software guy who hasn't used one for a few decades). I will get a hardware engineer more involved in an effort to resolve.

RE: nRF52832 SPI 4-Wire Master Issue with SPI Sample

Daniel Veilleux — Thu, 14 Jul 2016 23:59:04 GMT

RK - great feedback.

Mark - I am also confused by this 'contention' concept; it's the slave's job to drive the MISO pin. Also, as RK pointed out, most SPI slave devices will either clock out a status byte or garbage for the first byte of a transaction because they don't know what you want to do until they've read at least a byte of data. From the datasheet linked above:

""" bit 8-15 : data DO(7:0) (read mode). This is the data that is read from the device (MSb first). """

Bits 0-7 in read mode are garbage for this device.

RE: nRF52832 SPI 4-Wire Master Issue with SPI Sample

RK — Thu, 14 Jul 2016 23:34:43 GMT

"there appears to be contention on the MISO, MOSI and Clock lines." is really totally meaningless, it just doesn't say anything beyond "I don't understand the signals". The peripheral just doesn't produce signals with 1/2 voltages so either there's a connection issue on the board, and it would have to be a very odd one, or the scope's not showing the signal properly. The SPI module doesn't produce signals which look like that, whatever you do to it.

As to the rest, since SPI clocks data in at the same time it clocks data out, throwing away the first few received bytes is not unusual because the first few bytes are clocked in from the slave before it's received the bytes with the request, and those bytes are often either 0xFF or 0x00, ie with no data to send the slave just clocks out 1s or 0s. So that sounds completely usual to me.

RE: nRF52832 SPI 4-Wire Master Issue with SPI Sample

Mark J — Thu, 14 Jul 2016 20:45:57 GMT

RK - thanks for the response.

No DK used. This is a custom device with solid trace supporting VDD and Gnd connections between an nRF52832 and accelerometer.

Since posting, I have had some success using the driver. I am now reading 2 bytes (even though 1 is returned) and I am consistently getting 0xFF and then the byte that contains peripheral register data. I am also able to write peripheral register data and read back modifications. To get this, I changed the mode to "...Mode_0", set the speed to 8 Mbps and I am throwing out the first byte returned from the driver (always 0xFF).

I am still very concerned that I am seeing the scope output shown and will hope that someone from Nordic can offer a suggestion. Our hardware engineer has suggested that there appears to be contention on the MISO, MOSI and Clock lines.

RE: nRF52832 SPI 4-Wire Master Issue with SPI Sample

RK — Thu, 14 Jul 2016 03:56:22 GMT

Last time I had levels doing something silly like that I had a grounding issue, are you sure your dev board and your sensor have the same VDD and their grounds connected directly and firmly together? When I didn't have that right, the whole sensor chip floated up and down as GPIOs went high and low.

You should also fix your outstanding scope setup issue because it makes the results at least a little suspect.

SPI is a driven protocol, so pullups/pulldowns aren't required.