CMWX1ZZABZ-078 TxTimeout error

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Hello,

I have built a custom PCB which contains a few sensors and CMWX1ZZABZ-078 Murata chip. I also have a B-L072Z-LRWAN1 development board, on which I have been testing my code based on the projects provided by ST website (STM-CUBE PingPong project for example).

My project runs very well on the development board, but it does not send any data when run on 078 chip on my PCB. I debugged the project using SystemWorkbench and STLINK-V2 and found that after every Radio.Send() call, RadioEvents.TxTimeout is called. Ideally if the data is sent, TxDone should be called, which I guess is happening on the development board but not on my PCB.

Can someone help me figure out why this TxTimeout occurs? I have deciphered from the code that DIO0 pin should trigger a TxDone callback, and I am guessing that pin is internally connected to the mapped pin on STM32, but I don’t see it anywhere in documentation. Is this because of using 078 chip vs 091 chip which is on the development board?

Thanks for your help!

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A wild guess … How did you hook up TCXO_VDD ?

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Connected to PA12 and I have changed the define statement in mlm32l0xx_hw_conf.h file too. The error is still there.

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@GrumpyOldPizza I debugged a bit more and found out that the RegOpMode register never changes value from Sleep-mode (0x00) hence never goes into Tx mode or even Standby mode. Any idea why this might be happening?

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Naive question, can you read the chipID of SX1276, just to exclude SPI communication problems ?

I am asking, because out of reset RegOpMode should return 0x08. And all the code that you are dealing with would not touch this bit (no matter whether FSK or LoRa modem).

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@GrumpyOldPizza I am sorry for being unclear, the RegOpMode content is 0x88, of which last 3 bits are 000 which denote sleep state. I tried reading chipID and a few other registers and reading and writing registers via SPI is working fine.

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Ok, when do you read RegOpMode ? In TxTimeout, or where ?

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@GrumpyOldPizza I added a read statement in SX1276Send function, right after it calls SX1276SetStby. I also added a while loop which reads RegOpMode and keeps setting it to standby until it leaves sleep mode. The code is then stuck in the while loop.

I think there may be an issue with the VDD_TCXO connection (not soldered correctly perhaps). Would one be able to read and write to registers in that case (TXCO is 0 case)? And would the write to RegOpMode get reflected?

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SLEEP mode does not need the TCXO (or OSC), but STANDBY does (and any other mode but SLEEP). So that’s why the TCXO is a good candidate.

I can think about a bazillion other things that normally could go wrong, but those are all hardwired on the Murata module …

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@GrumpyOldPizza can we read if clock is being enabled using PH0 pin, connected to TCXO_OUT (Murata datasheet says that connection is optional, but I have added it on my board)?

Also, I checked multiple boards and all are facing the same issue hence I dont think this is an error in soldering. What other register settings could possibly affect this?

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On which GPIO did you put VDD_TCXO ? PA12 ? Did you check that it’s actually driven properly ? Or is PA12 by chance also used for USB ?