The big clock question | Cypress Semiconductor
The big clock question
This could apply equally to PSoC 3 as well as PSoC 5.
There is no doubt that the clock and timing systems in the PSoC 3 and 5 are impressive in their range of features and options. This flexibility comes at a price, though, because you need to configure a complex system correctly. Design descisions yout make at the outset might have implications down the road. You might also need some good fortune and a bit of clairvoyence to get it right first time!
Yes, I'm joking a little bit, but I thought I'd pose the question - whats the best practise for configuring the clock system?
For instance, do you just leave everything at the default and hope for the best?
When do you decide to use an external crystal, or oscillator, rather then the internal oscillator?
Application note AN54439 gives some great information on configuring PSOC3 and 5 for external crystal or ceramic resonator.
If your clients are anything like mine, you may not even know at the original design stage what options you'll need. You may initially think that the internal oscillator will be good enough, but then later the client asks you to add a USB HID interface, or a UART with low tolerance, or maybe add some requirement for precise timing of incoming signals. This happened to me recently when the cllient decided that the product which was already near production stage should suddenly have a requirment for a USB HIB interface. Fortunately in this instance I had already specified an external 24MHz crystal.
So, how do you do yours? And have you ever been caught out by using an internal oscillator and wished you'd used a crystal, (in any architecture - not just PSoC)?