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Both my microcontrollers on my project (dsPIC33FJ128GP804 and PIC24FJ64GA004) support JTAG boundary scan testing. Should I wire these up and expose a JTAG port for hackers? The product is intended to be open hardware and as such be modified. ICSP and ICD ports will also be exposed. Of course these ports and traces take up space - so is it worth it? Would people be able to use them with basic PIC micros?

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I'd say you should ask your potential users that. Since it's open hardware, JTAG would add to the feeling of openness, but if your target audience isn't interested, it would be a waste of time. – AndrejaKo Dec 10 '10 at 12:48
@AndrejaKo, I'd ask, but I'm selling to both EE's and non-EE's - the EE's will probably say "yes please", the non-EE's will probably say "I don't care." – Thomas O Dec 10 '10 at 12:59
As I feared. Unfortunately, I don't have anything smart to say. :( – AndrejaKo Dec 10 '10 at 13:05
This is a rather subjective and localized question. The answers will all depend on who your audience is and what could be done in your particular application. If you don't know what all a JTAG connector can do for you then you can ask that and then decide on your own if the features that you get are worth it. – Kellenjb Dec 11 '10 at 21:53

4 Answers

up vote 10 down vote accepted

How expensive is half a square inch of board space? Bring out the traces to some small pitch pads. Those who are interested can solder their own header adapter.

(EE who says "yes please")

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We do this even on products that are never intended to be modified by the end user. Makes them easier to debug if something goes wrong in the field. Connector is expensive, so we just leave the pads. – AdamShiemke Dec 10 '10 at 15:18
Good idea. I'm going to do this as well. – tyblu Dec 10 '10 at 18:43
up vote 7 down vote

JTAG is very rarely used with those devices. All you need is the usual connector for an ICD 2/3 or PICkit.

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Agree. I've never used the JTAG interface on any of my PIC projects. The ICSP interface is quite adequate for debugging via MPLAB. – tcrosley Dec 10 '10 at 13:45
up vote 0 down vote

Yes, you should. It can be used to check connections between the chips. If there are a lot of such connections, it can really help. If they mainly go to other chips w/o JTAG (e.g. memories), then it won't be as helpful.

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up vote -1 down vote

These pins will surely be needed for the firmware debugging/loading.

You could always bring them out onto a section of the board that can be snapped off before delivery/installation. This means that the developer has access to the connector/debug interfaces that are absent from the final product. If you place the debug traces on an inner board layer then this will make the hacker's life more difficult but, assuming that you have not disabled the JTAG in the processor, they will always have access to the device pins and so to the interface.

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The ICSP headers are used for programming, not JTAG... unless I'm missing something(?) – Thomas O Dec 10 '10 at 13:21

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