AD7731

[TL]

I'm working on the AD7731 (24 bit sigma delta ADC) but am having 2 problems:

1. After I configured the filter and mode registers, and performed calibrations, the contents of the status register were read but it is wrong because the STEADY bit is 1 instead of 0. This means the internal AD7731 filter is not settled (i.e. not steady).

2. In bipolar mode, Vref=2.5V and input vdiff = 0V (AIN1=2.5V, AIN2=2.5V), the DOUT pin sends out 16,777,215 instead of 8,388,608 (mid count).

Has anyone had the above problems? Has anyone got the AD7731 working?

Thanks.

[PCM programmer]

One possible reason for these two symptoms is that your software
driver is "off by 1". It's losing the first bit (the MSB), so everything
is shifted left by 1 bit position. This could also account for the \STDY
bit being in a constant high state. Because of the left-shift, you would
not be reading the correct bit.

Another possibility is that you have the chip in the wrong mode.
The \STDY bit acts differently if the chip is in FASTStep™ mode.

[TL]

Thanks PCM Programmer for replying.

After more investigation, I found out the actual cause was due to the mode register set incorrectly, hence the 2 problems found.

[joven]

Hi TL

Can you post the driver?

Thanks