Hello!
I´m a newbie and trying to understand in the LPC1766-STK schematic what are several components (aparently resistors) with a value of "NA" . They appear int the reset circuit (R140), RS232 (R87,R78) and also in the USB_host and device, in this case with a little "0R" inside the component rectangle (so far these are the ones that I´ve found). Any clue, please?
Thanks in advance for any info!
Best wishes,
LuizF
Hey LuizF,
NA component stands for a component that is "Not Assembled" during production. This means that there are pads provided but the element is not placed on purpose. Now, there are different reasons not to mount components but most commonly this is done because:
1. The board behaves better without that component (usually in later board revisions).
2. The component is optional according to the microcontroller and active IC datasheets - so we have provided the pad if somebody wants to experiment.
3. The components that is NA might serve as a jumper altering the behavior of the board (or the behavior of a near component or signal line).
4. The component pad was used as a testing pad.
and so on!
You should be very certain why we didn't place elements marked as NA before attempting to add such. Generally speaking, if you don't understand why there are elements missing it might be a good idea not to solder anything.
OR resistors serve similar purpose. They are placed instead of jumpers. Please refer to the wiki article: http://en.wikipedia.org/wiki/Zero-ohm_link (http://en.wikipedia.org/wiki/Zero-ohm_link)
Best regards,
Lub/OLIMEX
Dear Lub/OLIMEX,
thank you very much for the clear answer.
Best regards,
LuizF