Here's an excerpt from AN54439 about external crystal oscillators:
Using an External Clock Signal on the ECO Pins
If the MHz or kHz ECO is not being used, an external clock signal may be routed onto the ECO clock nets using the kHz or MHz crystal input pins. This allows the use of these clock nets in place of the usual DSI clock net in the clock tree. External clocks can be routed into the part through the kHz and MHz XtalIn pins. The XtalOut pins should be allowed to float. Ideally, the external signals should be rail-to-rail sine or square waves. If the amplitude of the signals is too low, they may not be properly translated into digital signals. These signals must be within the frequency ratings of the ECOs, either at 32.768 kHz or 4-25 MHz.
External clocks can also be routed into the part using the GPIOs. For more details, see AN60631 - PSoC® 3 and PSoC 5LP Clocking Resources.
I want to use MEMS oscillators for both the MHz ECO and the 32khz ECO. It sounds like I can tie them right to the input of each ECO, but it doesn't say anything about how I would need to set it up in Creator. It has all the parameters for fine tuning the crystal such as fault recovery, amplitude adjustment, and reference levels. Anyone know what settings I would use in this case? Also, it says it should be a rail to rail input, but which rail are we talking about? I'm planning on using 5V for all but one or two ports, but the MEMS oscillators seem to be 3.3V max most of the time. It seems like the VDDIO for the port where the ECO pins are located would not have any effect since the pin is being used in a different mode, right? Some guidance would be greatly appreciated.
The ECOs are oscillator circuits needing an external crystal. Thats what the configuration is for. Your MEMS oscillators are an standalone component. So you need to configure PSoC for just using an external clock signal. I know that its possible for the MHz ECO, but I'm not so sure about the kHz ECO (and I lack the time now to check). Just look in the clock configuration screen...
You might contact max (author of ap notes) directly, and post back here for the
rest of the forum.
Neither ap note discusses if ECO amp is a standard logic inverter or a specific amp
design, so anwering R-R question (my guess is Vssd to Vddd) would be just that, a
guess, and should not be considered sufficient.
You might suggest max rev his ap note(s) to include the basic questions you are asking.
To elaborate a little bit deeper:
For the 32 Khz, you will be coming thru the internal route to the
amp designed for oscillation, if its not a standard CMOS inverter
like used in GPIO structures, its levels/bias may need to be addressed,
need to be confirmed with max.
I will email max and point him to this thread, and see what we get.
I have not heard either, glad you posted a CASE, maybe I should have done that from the
getgo as we never know if author still with company.
Here's the response to my case. Looks like, I'm good to go.
MHz XTAL pins are also GPIOs. Hence they can be used as normal GPIOs. Disable the ECO in the .cydwr -> clock tree and select the Digital Signal and source the other clocks from Digital clock. The procedure is same as in the AN60631.
If the peak to peak amplitude of the MEMS oscillator is 3.3 V or more, it should work because internally the signal gets into the clock tree where a level shift will reduced it to 1.8 V peak to peak.
For KHz ECO, you need to enable the KHZ ECO in the clock tree and just connect the external MEMS oscillator to the KHz ECO input. No setting is required for this in Creator.
So summary is MHz ECO needs to be disabled and the same input pin can be used to give external digital clock. But KHz ECO needs to be enabled and connect external clock to the input pin of KHz ECO in PSoC.
I tested both of the clocks int the above mentioned configuration and found it to be working.