Problems of reading with LMP 90100

Alexander,


It looks like you're having problems with the SPI control of the LMP90100, so let's start by looking at the commands that your sending. For both the write to the auxiliary control register (ADC_AUXCN) and the read from the ADC_DOUT register, I'd like to see an oscilloscope plot of the SPI lines.

Here's what I think the SPI transmissions should look like:

1. For the first control sequence to set the IB1 and IB2 magnitudes, you need to set the ADC_AUXCN:RTD_CUR_SEL bits.

Transaction 1 - URA setup for ADC_AUXCN (ADDR 0x12)
0x10 for write address
0x01 for URA

Transaction 2 - write 1 byte (of 0x0A for 1000uA) to ADC_AUXCN
0x02 for write data, 1 byte, 0x2 for LRA
0x0A to set 1000uA

2. To read the data back from ADC_DOUT, here's a method just using the register address read. I'll keep in Transaction 1 to be complete.

Transaction 1 - URA setup for ADC_DOUT (ADDR 0x1A)
0x10 for write address
0x01 for URA

Transaction 2 - read 3 bytes (starting at 0x1A)
0xCA for read data, 3 bytes, 0xA for LRA
Clock out 3 data bytes

You may need to track DRDYB to indicate when fresh data is available. You can read through different cases of using the DRDYB for reading data. This is covered in the datasheet, starting in section 9.5.8 on page 35 going to 9.5.11.

Additionally, there is a mode with data only read transaction, where you can get the data directly from the bus without an instruction byte. This is discussed in 9.5.12 on page 38.

Regardless, if you continue to have problems communicating with the LMP90100, get an oscilloscope plot of the SPI communication and post the result here. We can review it and see where the problem might be.


Joseph Wu