LMX2592: Cannot configure chip via SPI in VHDL

Cameron Seamans

Part Number: LMX2592

Hello,

I am trying to configure the LMX2592 via SPI on a custom board. I know the board works, because it is the HiTech Global HTG-ZRF8, and a colleague successfully programmed the chip via a Linux application. I am using VHDL on a Xilinx Zynq Ultrascale+ RFSoC. I can see the SPI communications going into the LMX2592 with an oscilloscope, and I can see what I believe to be the correct SPI transactions with Vivado's Internal Logic Analyzer (timing of SCLK/SS/MOSI look right according to the LMX datasheet), but there is no output from the LMX. Additionally, I have added a readback pack at the end just to test if I can even read something back from the LMX, but the MISO line just stays low. So I am not sure what the issue is. I have attached screenshots of a sample 24-bit packet/clock/slave-select, as well as the set of addresses/data that I am writing.

Thanks

over 5 years ago

0 Noel Fung over 5 years ago

TI__Guru** 107030 points

Hi Cameron,

What is the reference clock frequency and the intended output frequency in your code?

BTW, the MUXout pin is never hi-Z, do not connect it to the standard SPI MISO bus if more than one devices are already connected to the same bus.

0 Cameron Seamans over 5 years ago in reply to Noel Fung

Prodigy 65 points

Hello Noel,

The reference clock frequency is 122.88 MHz and the intended output frequency is 122.88 MHz. There is only the one SPI slave on the bus, and one master.

0 Noel Fung over 5 years ago in reply to Cameron Seamans

TI__Guru** 107030 points

Hi Cameron,

Please try with the following suggestions.

0 Cameron Seamans over 5 years ago in reply to Noel Fung

Prodigy 65 points

Thanks for the suggestion Noel. I just tried that, and I still see no output from the LMX. So I have to believe that there is an issue with my SPI transactions, but I have checked the LMX2592 datasheet and compared that to the SCLK/MOSI/SS waveforms I see on my oscilloscope, and I feel as though all of the timing and polarity is correct. Any other ideas?

0 Noel Fung over 5 years ago in reply to Cameron Seamans

TI__Guru** 107030 points

Hi Cameron,

Let's try to see if the SPI is through.

1. Vcc power up the device.

2. program 0x00221D to power down the device.

If you do not see current change, that means SPI did not work.

Clock & timing

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LMX2592: Cannot configure chip via SPI in VHDL