STW81200 does not answer on MISO line

[mariecurie]

Hi, 

Im interfacing STW81200 with SPI without no success. I do have the following questions:

What the SPI mode? Its not clear on the datasheet. It seems that CPOL = 1, and CPHA = 1.

In either way, I have tested the communication with several modes and none of them works.

On the MCU side, which is the one that will act as a master on spi, whats the configuration for the GPIO pin? Im using STM32L412 and I have set the MISO as an alternate function with push pull open drain and this does not work either.

I can confirm that the SPI signal for SCLK and MOSI its working because the data is being pushed out of the pins. Please see the logic analyzer graphs, but MOSI line is not responding.

Im following the datasheet section Example of register programming, its required when programming in SPI to have enabled a reference clock or this can be absent? 

Also, when the MCU is configuring for spi, it clear HW_PD, PD_RF_1 pins.

[Chris21]

The diagram in the datasheet implies that LE should be set high after 32 bits, each register access likely needs LE to go low, then high.

[mariecurie]

> The diagram in the datasheet implies that LE should be set high after 32 bits, each register access likely needs LE to go low, then high.

 I can see this on the datasheet. Thanks. However, this will be valid for the next request on accessing registers. 

I removed the write register transaction and leave only the read transaction, where at the end of this reading, LE goes high, then low. But the result is the same.

Please see image attached.

[TDK]

Are you following the power on sequence exactly?

[mariecurie]

> Are you following the power on sequence exactly?

Sort of because Im missing some information that does not allow me to completely verify that the power sequence is correct.

1. I measured this with an oscilloscope and all the inputs are receiving 5 V. Passed.

2. There is no way for me to certify this since I dont know what are the expected values to be read on these LDO. 

3. Currently the board I have, does NOT have the reference clock signal and this is one of the questions I made. This is my first time interacting with a synthesizer and Im not really sure if you need to have some signal in place before actually communicate through SPI. 

Based on this diagram, I can somehow infer that the spi block communication is separated from the rf stage. Please see spi-and-reference-signal-block.png

4. By the time this step is about to be made, 50 ms has elapsed since powering up the ic. I initially tried to do a write transfer on ST9 as in previous screenshots, but as this is a writing, I dont have any way to certify that the writing transfer is successful without actually getting back from the ic, so I tried to read the device id register ST11, without not having success. So, this step has not been made following exactly what it says because of my uncertainty of not know that ic is receiving the data. 

Maybe I should try to follow exactly as its stated and see if when reading on ST11, I will get a response. 

Maybe, all the steps below 5 needs to be made in order for the ic to reply back on ST11 as its stated on step 5. 

[TDK]

> Maybe I should try to follow exactly as its stated and see if when reading on ST11, I will get a response. 

That seems like the best approach, especially as you are running into issues.

[AScha.3 · Accepted solution]

Hi,

>its required when programming in SPI to have enabled a reference clock or this can be absent? 

because its a Wide Band Synthesizer , it needs a clock anyway, to do something useful.

So give it the needed reference clock first.

[mariecurie]

During the last couple of days I implemented first the whole transfer that its given in section 7.17 of the data sheet with no success. 

After that, I started to work on some parts of the circuit that were in charge of providing the reference clock signal as suggested by @AScha.3 and it has been proved that STW81200 indeed needs the reference clock signal to be able to reply through SPI.

The image attached is when the ic replies back when reading device id register.

Thanks everyone,