Content originally posted in LPCWare by IanB on Sat Feb 15 02:35:51 MST 2014
Twelve wire interface, thirteen wire interface, twenty wire interface - getting silly - time to stop before someone mentions thousand wire interface.
This is what it says in the LPC111x data sheet:
"27.6.2 Debug connections
For debugging purposes, it is useful to provide access to the ISP entry pin PIO0_1. This
pin can be used to recover the part from configurations which would disable the SWD port
such as improper PLL configuration, reconfiguration of SWD pins as ADC inputs, entry
into Deep power-down mode out of reset, etc. This pin can be used for other functions
such as GPIO, but it should not be held low on power-up or reset."
Then there is a diagram showing SWDIO, SWCLK, VDD, VSS and RESET (but not PIO0_1).
One thing that I have noted is that in the days of DIL packages, the extra cost of buying the device with more pins was quite high, so it was well worth designing around the device with the smallest possible number of pins.
With the LQFP and similar packages the difference in cost between 32 pins, 48 pins and 64 pins is not great, and it is probably worth spending the extra few pence to accommodate all six pins of the two-wire debug!
Also, if I do manage to program into a state I coax it out of with the debugger, there is always the option of getting out the hot-air SMD rework station and replacing the IC - it's only a quid.
