ADS1147: Do any SPI "Sync" commands actually work?

Eric,


I've never specifically tested these reset conditions myself, but I'm quite sure that the datasheet is correct. From other customer's use of this device, it should work this way, or a lot of the multiplexed channel applications that I've seen would have problems with operation. In a write to the device for one of the MUX0, VBIAS, MUX1, or SYS0 registers, it shouldn't complete the conversion, it should change the setting and start the new conversion.

I would start by looking at the communications with a logic analyzer and doing a simple test. I would simply let the part run, continuously converting, and observe the /DRDY pin. Then, issue a SYNC command and see how the /DRDY timing is affected. If you have something like a Saleae logic analyzer, I can take the data and use their software to look at the communication. I would record /CS, DIN, DOUT, SCLK, and /DRDY.

If this works, I would look at the /DRDY behavior after a write to the first four registers. I should be something different than the previous register contents. I think that the device does check to see if the state changes from the register write.

Other than that, do you have any scope photos to show that the timing isn't changing after the write or the SYNC? If you can get a shot, please post it or even better post the data from a Saleae logic analyzer. I'm not certain what other formats I can take, so some sort of screen shot might be best.


Joseph Wu

Thanks....

Indeed, it would help very much if my code ensured that the CS (Chip Select) pin was low when I wrote the SPI data....I found that out once I started cycling channels...

Once that issue is taken care of, the chip works as advertised.

Eric Christenson

P.S. The code on my CPU got buggy because I need to be able to interrupt communications on the port asynchronously for a higher priority device on the same port, and I had no code review to pick up that the chip deselect at the end of the routine that writes to a register did not have a corresponding chip select at the beginning, thus asking for trouble! I'm re-organizing and re-writing that code today.


P.P.S. The datasheet says chip restarts conversion on EVERY write to those registers, change or not. That's not unreasonable.

P.P.P.S. Saleae logic analyzer? I'm using MPLAB REAL ICE and a two-channel digital scope, and mainly checking on the CS line.