setup ADS1240E using pic18f46k22

Hi Mahesh,

Since you're able to look at the waveforms with a DSO for the communication to the ADS1240, could you please post a screen shot of this?

I would write commands one register at a time and post the signals for /CS, SCLK, DIN and maybe DOUT of each communication.  Start with the change in the data rate and we'll see if there are any problems.

Joseph Wu

Dear sir,

                this are some screenshots of code in which i have send read command to ADS1240E and reply from it..

           this waveforms taken across pins of ADS1240E. if you required code please reply me .

hi sir,

  here i have attached waveforms for CS,DIN and SCLK. i am just send read data command continuously to read DOR resistors.so kindly tell me my waveforms are ok or not.

Mahesh,


I need a scope shot that I can read the bit transactions. In my last post, I mentioned that I'd like to see them on the 2.5us or 5us scale. That way, I can actually read the bits being clocked into the device.

At this point, I can only see enough to read the bits from the fourth photo in your most recent post. I believe that it shows the last two bytes of the transaction, which appear to be 0x01 and 0x00. Could you confirm that is what you intended to write to the last two bytes?

Also, it's still hard to read, but the DIN looks a bit skewed. If you look at the first rising edge of DIN from the same photo looks like it take a long time to rise. You may want a closer look at it to make sure that the DIN rises fully before the falling edge of SCLK.

If you are having problems writing to a register could you get a scope shot of a WREG command to set the configuration? I think these photos show only RDATA (I can't be sure, but most look like they start with 0x01).

I would also follow that up with a RREG command to see if the data that was written into the device is read out properly. In both the RREG command and the WREG command, If you can, use the RREG command to read back the entire register space from the device. That part you can report back in text.


Joseph Wu

hi sir,

   thank for  your reply. here i have attached waveforms.

This waveforms for RDATA command.

 This waveforms are for RREG command for SET UP register.

This waveforms are for RREG command for MUX register.

Mahesh,


If you are able to send a schematic, would you be willing to post it? In particular, I'd like to know if the POL pin is low.

If it is, then based on the scope photos, you have the wrong type of SPI running. If POL=0, then the data should be set up on the rising edge of the SCLK, and clocked into the device on the falling edge of SCLK. The way you have shown it, the data is setup on the previous falling clock edge, and clocked into the device on the rising clock edge. The way you have shown it could work if POL=1, but the SCLK still needs to dwells low, so that reading out the data, your DOUT sets up on the falling edge of SCLK.

Look at Diagram 1 of the ADS1240 datasheet and note the timing between rising and falling edges of SCLK and DIN. It should guide you to the correct SPI clocking.


Joseph Wu

hi sir,

here I have attached my schematic.

sir , i have tested waveforms for RREG command to read SET UP, MUX and ACR registers. data for MUX and ACR registers is as per setting. but for SET UP register i am getting constant data 20H (32 decimal). why it is so.7827.SCHEMATIC1 _ PAGE1.pdf

Mahesh,

The setup register should read X0h, where X is programmed to a particular value as an ID for the factory. This should be the default value. In your case, are you trying to program it to a different value? If you are, then what value are you trying to program it to?

I would try to record the same scope photo showing the write transaction if you are having problems with it. Note that in my previous post, I mentioned that I thought your SPI transaction is wrong and you are trying to clock in data with the wrong edge of SCLK.

Let me know if that is the case. Also, if you are trying to write to the register, show the write transaction in a similar format so I can read the bits.

Joseph Wu

hi sir,

     i have tested waveforms for RREG command to read SET UP , MUX and ACR resistors. if i have changed set value of ACR and MUX resistors and read it then i have got right values of both. but in case of SET UP resitor i am able read same data only i.e. 20H.

1) this waveforms are for SET UP resistor with RREG command.

2)  this waveforms are for MUX resistor with RREG command.
 where i have read output data as 01H

3) this waveforms are for ACR resistor with RREG command.and here i am able to read 02H from ACR resistor

now my SCLK speed is 250KHz and tell me that i am getting Right waveforms or not. also there was problem in my SPI set up code i have made changes and then take this snapshots.

.

hi sir,

 sir i have  provide 0.5V supply to i/p of  ADS1240E analog pins. and test readings on DSO.
  i have taken VREF as 2V as per schematic i have attached previously.  i have calculated decimal value for data out from ADS1240E. it seems to be correct.  tell me that digital o/p of ADS1240E is 2's compliment or hex. also vref will remain same if we change i/p from Volts to micro volt.

i have one more question that what relation between VREF and Gain. if i have to sense o/p of load cell having o/p range 1mV/V , excitation voltage is 5V . what should be gain. and how should i calculate my least count for load cell using Vref.