Pmod AD1 and AD2

[cmeuchel]

Looking at the layout, the AD1 seems to have differential inputs while the AD2 seems to have single ended inputs.  Can the AD2 be programmed to have two differential inputs?  How many units can I put on an SPI bus?

[JColvin]

Hi @cmeuchel,

Neither the Pmod AD1 nor the Pmod AD2 have differential inputs. The Pmod AD1 inputs A0 and A1 go to two separate ADC channels and otherwise use common ground as a reference.

In principle for both Pmods, you could compare separate inputs to each other after the data has been received by the host board, though you would not be able to use different "grounds".

As for the number of units you can put on a SPI bus for the Pmod AD1 (the Pmod AD2 is I2C based), you are in theory limited by how many separate CS lines you provide, one for each Pmod, since you could share the two data lines and single clock line between all Pmods as they would not communicate with the host board as long as their CS line is not pulled to a logic low state. With that in mind, the number of modules you can use will be limited by the I/O available on your host board as well as the desired data rate you wish to achieve between all of your modules.

Let me know if you have any questions about this.

Thanks,
JColvin