Could someone please explain to me the difference between what seems like much all the same thing…
I see in the reference sheet for the breakout board these:
Single Ended IO - I understand how this is different than → Differential IO
Differential IO - I understand how this is different than → Single Ended IO
Analog Input - How is this different than other 2 ^
Analog Supply - What does this do ?
Thanks,
JT
Single Ended IO = Single Ended Digital IO (eg. LVCMOS)
Differential IO = Differential Digital IO (eg. LVDS)
Analog Input = Dedicated differential inputs to an XADC (v_p, v_n). Different than the other 2 by virtue of being analog instead of digital.
Analog Supply = 17 inputs (on Bank B) connected to an on-chip multiplexer which can be routed to an XADC [Au]
One note: except for the dedicated analog input, the other analog pins can also be used as digital IO.
So if I understand what you are saying…
Single Ended IO = Can be Analog or Digital
Differential IO = Can be Analog or Digital
Analog Input = Dedicated differential inputs to an XADC (v_p, v_n). Different than the other 2 by virtue of being analog instead of digital.
Analog Supply = Can be Analog or Digital
The Single Ended and Differential IO are only digital (why I added and underlined Digital in my reply).
As pointed out, the pins labeled Analog Supply can in fact be used as digital pins if you wish. There are a few caveats if you use some of these pins as analog inputs and others as digital lines, so personally I’d avoid it unless I ran out of dedicated digital lines.
I guess I do not understand how you would use Differential Digital, most digital are: 5v, 3.3v, 1.8v and GND.
Or maybe I don’t get it.
First, remember that signals are just voltages on wires, the distinction between analog and digital is all in how we measure and interpret those signals. Differential inputs are useful for analog signals because of the reduction in common-mode noise. The same is true for digital signals, you can even consider digital signals to be analog signals that we measure with a 1-bit ADC. You can have all of your favorite digital levels (5V, 3.3V, 1.8V,…) in a differential digital system based on the reference voltage used by the 1-bit ADC (aka a comparator).
Reducing the noise in a digital system (ie. by rejecting common-mode noise), will in principle allow you to reduce the level required to specify a high signal. This not only reduces power consumption greatly, but it also increases the speed. Stray capacitance (cables for example) imposes a limit on the slew rate (Volts/sec), therefore, reducing the voltage swings leads to shorter propagation delays. The cost is that there can no longer be a single shared digital ground and you have to keep in mind that impedance matching becomes important as the speed goes up.
For an example, study the LVDS standard, a commonly used differential digital standard. I have an old LVDS display that I will someday connect and play with, but in the meantime it is very convenient that we can connect the device directly instead of interfacing with a CMOS to LVDS line driver. If you want to play with it, a lot of high-speed ADCs have LVDS interfaces.