LMX2820EVM: LMX2820EVM

Hi Kuowei,

Could you provide your schematic? I am particular interested in the SPI interface and MUXOUT interface. Do you have any RC filter on these interfaces?

This is EVM board, I refers to Page 10 and 11 of the document. Link is https://www.ti.com/lit/ug/snau246a/snau246a.pdf?ts=1689827307603&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FLMX2820EVM%253Flogin-check%253Dtrue 

Hi Kuowei,

I don't have this problem with both 12.5MHz or 25MHz SPI.

Could you verify that you also cannot readback with TICS Pro and USB2ANY?

I can use TICS Pro with USB2ANY, but the SPI only up to 125KHz

  Is it probably my LMX2820EVM broken or somthing else?

Hi Kuowei,

Readback is normal and you got the right signal, that means the board is normal. TICS Pro SPI is 125kHz, that is correct.

Please verify if this is a measurement issue. When we measure the readback signal at TP_MUXOUT, the probe tip is connected to the test point and the probe ground should be connected to the nearby ground with a short cable. If the original probe ground cable is too long, think about how to make it shorter. 

I try that a master using SPI interface to communicate with LMX2820EVM.

Write operation is correct, but read operation is incorrect, so I don't think that ground too long to cause the MUXOUT signal issue. 

Hi Kuwwei,

Could you lower master SPI speed to see if the master can read? 

Your measured readback waveform is distorted seriously, there is a series 33Ω resistor on the EVM, do you have any shunt capacitor on the master side?

6.25M can read, 12.5M can't read.

No any shunt capacitor on the master, but this is used signal filter, my issue is voltage too low. 

Hi Kuowei,

I don't have any idea what when wrong, this is a very simple connection.

The last suggestion I can provide is, program R4[1] = 1. That is, program R4 = 0x04 4206. If this method did not work, then I have no other solution.