General Guidelines for Hardware Design [Interesting Stories]

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====== General Guidelines for Hardware Design ======

===== Architecture =====

Architecture is a big topic. The purpose here is not to cover the entire topic. Want to point it out that it pays to begin with interface and connector choices.

===== Power =====

  - Begin with a power tree that include voltage/current requirements.
  - Keep power sequence in mind for both turn-on and turn-off.
    - most of the digital ICs don't like to be back biased meaning voltage on any of its pins goes beyond VCC. This can happen during power-on when VCC is low.
  - Reverse plug-in protection can be a user friendly feature if the power comes from external.

===== Reset =====

  - Similar to power, please consider which IC needs to come up first by releasing reset in a specific sequence.
  - It is also necessary to hold the reset until VCC stabilizes if the IC does not have built-in power-on reset feature (most modern ICs have POR).

===== Clock =====

  - Clock tree is a common design document (just like power tree) to document how the clock is generated and distributed.

===== Debug Features =====

  - Have clear mind how to program and debug the circuit. JTAG is standard but can be complicated and requires expensive debugger.
  - DEBUG UART can be much simpler for small MCUs.
  - It is also common to have two wire proprietary debug interfaces. Consider referencing to EVK how programming/debug is implemented. It is also a cheap way to use EVK debug feature to program/debug your own design without having to purchase a separate debugger.
  - It is very helpful to have LEDs to show visual sign of life. E.g. to indicate power is up, or to indicate a GPIO can wiggle.
  - The general bring-up procedure is to check Power, Reset & Clock. 

===== Power Measurement Features =====

  - MCU power consumption is very much dependent on the program that is running. Characterizing power consumption is a career by itself.
  - It can be very handy to have instruments built-in to measure power rail voltage/current.
  - CPU powers (AMD, Intel) are required to have telemetry reporting

===== ESD Protection =====

  - Don't forget to have ESD protection elements for external accessible interfaces.

===== EMI Consideration =====

  - Good layout
  - Filtering
  - Shielding
  - Grounding