> is it possible to have just a few (e.g. 6) signal to program
 > an ARM chip on board if debugging is not possible?

Most ARM chips have an on-board bootloader, so you can program (not 
debug) with just GND, RX, TX, bootload enable, reset.

Newer ARM chips (Cortex only?) have IIRC a 1-wire debug interface, I 
don't know the details of that one.

For the 20-pin box header: check the circuit of any board that has this 
header: half the pins are ground. Remember PIC ICSP problems with 
crosstalk from PGD to PGC? Some magic-value capacitor on the PGC often 
solves it. For the ARM, with a 20-wire flatcable, there are lots of 
in-between ground lines. Sensible design for medium-length cables.

-- 

Wouter van Ooijen

-- -------------------------------------------
Van Ooijen Technische Informatica: www.voti.nl
consultancy, development, PICmicro products
docent Hogeschool van Utrecht: www.voti.nl/hvu

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