CCS/ADS127L01: ADS127L01: can not get the data from ADS127L01 by spi of C5535

user3475476

Part Number: ADS127L01
Other Parts Discussed in Thread: , TMS320C5535

Tool/software: Code Composer Studio

i'm using C5535 to get the data from ADS127L01 by spi interface. Now I can read the device Id reg and mode reg well from the ADS127L01. But with the same code, I can't read any data from ADS127L01. The STRAT pin is hold high and I can see the DRDY remains low but pulses high for a duration of 2 · t CLK. The following is the snapshot.

red is spi clk, green is the spi out of adc, blue is drdy. just no thing out from adc. Could you give me some help? why no data out from adc? Thanks

over 8 years ago

0 Tom Hendrick over 8 years ago

TI__Guru**** 181521 points

Hi user3475476!

Welcome to our e2e forum! DRDY should go low when the conversion is complete and then rise after the first SCLK falling edge (this is depicted in Figure 91 of the ADS127L01 datasheet) and seems to be 'normal' in the screen shot you provided. To try and figure out what might be going on with the output data, I would like to start off by getting some additional detail on your hardware. Is this your own custom PCB or is it one of our evaluation modules for the ADS127L01? If it is custom hardware, can you provide a schematic of the detail surrounding the ADS127L01?

0 user3475476 over 8 years ago in reply to Tom Hendrick

Prodigy 90 points

hi Tom,
thanks for your quick reply. Actually, I am using the ADS127L01 evaluation board and C5535 evaluation board and connecting them by spi interface. The ppmode mode 1 and cs2 spi are used. Spi out , spi in, sclk, drdy, cs and ground are connecting over these two boards.

0 Tom Hendrick over 8 years ago in reply to user3475476

TI__Guru**** 181521 points

Hi!

Are you connected into the debug header (J6)?

0 user3475476 over 8 years ago in reply to Tom Hendrick

Prodigy 90 points

yes， the c5535 spi interface is connected into J6. Also, the oscilloscope is connected into J6 to capture the signal.

0 Tom Hendrick over 8 years ago in reply to user3475476

TI__Guru**** 181521 points

Thank you for the additional detail! Can you please verify for us if the EVM works properly when using the ADS127L01EVM stand-alone, as it was originally shipped? Can you probe J6 and see if the SDO is present under this condition?

0 user3475476 over 7 years ago in reply to Tom Hendrick

Prodigy 90 points

I will capture the signal as soon as possible.

By the way, as the picture, when reading adc 4 bytes, the read sclk is not continuous but spaced with several clks. Is that correct?

0 Tom Hendrick over 7 years ago in reply to user3475476

TI__Guru**** 181521 points

Hi there!

The pauses between the SCLK bursts are a function of your micro-controller. I am not familiar enough with the TMS320C5535 to tell you what options there are to reduce or possibly eliminate those gaps. You could post a query to the C5000 Ultra Low Power DSP Forum and ask the experts there if there is anyway to avoid them.

0 user3475476 over 7 years ago in reply to Tom Hendrick

Prodigy 90 points

hi Tom,
I mean if the micro-controller gives the sclk to adc that way, the micro-controller can get the correct data? or the adc MUST require the sclk is continuous otherwise no correct data could send out?

0 Tom Hendrick over 7 years ago in reply to user3475476

TI__Guru**** 181521 points

The micro would recieve 4 bytes, one for each transfer with the first three being conversion results. In your uC code, you would have to shift the first two and then concatenate to get the proper 24-bit result. The last byte would be the STATUS.

0 user3475476 over 7 years ago in reply to Tom Hendrick

Prodigy 90 points

hi tom，

sorry for the late picture. Limited to the number of the oscilloscope probes, only two signals can be captured once. I think the signals of the adc demo board is OK.

this is the clk and spi

this is clk and spi out

this is clk and cs

this is clk and drdy

0 Tom Hendrick over 7 years ago in reply to user3475476

TI__Guru**** 181521 points

Great! So at least you are able to confirm that SDO comes from the ADS127L01 when it's configured for the default EVM operation. You might try connecting everything up the way you had it when evaluating the C5535, but leave the SDO open and see if you still see data on the scope. From there, just start looking at the rest of the connections between the boards and see if anything is connected wrong.

0 Tom Hendrick over 7 years ago in reply to Tom Hendrick

TI__Guru**** 181521 points

Hi there!

Have you been able to resolve the SPI read problem on the C5535?

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CCS/ADS127L01: ADS127L01: can not get the data from ADS127L01 by spi of C5535