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Sat Jun 6 12:51:14 CEST 2009

debugger interface

Problem: I've got my boards standardized on the 1x6 serial port header
for the FTDI.  I'd like to keep this working because it's damn
convenient.  Now the problem is, 6 pin headers are not really
standard.. You can find 2x5 everywhere.  And I have plenty of
flatcable to go with it..

How to combine?

A 2x5 header could exhibit these 10 signals:

POW VDD
POW GND
SER TX
SER RX
ICD MCLR
ICD PGD
ICD PGC
ICD PGM
I2C SD
I2C SC

SPI is best carried over a separate channel since it has 3+1 lines.
It's more for fast comm anyway.. This bus is for debug.

Can this be made compatible with ICD and TTLSERIAL pinouts by plugging
them in some fashion?  It can be made to work for either the SER or
the ICD, but not both.  Ser is probably more important.  I can use an
adaptor for ICD.


GND  PGD
MCLR PGC
VDD  PGM
RX   SD
TX   SC

Can the brown line (MCLR) be driven from the TTLSERIAL?  This would
enable target reset. It's CTS (see [1]) which is an input, so this
won't work.  OTOH, this means that it won't be asserted so it's ok to
connect it to a reset pullup.

Doing it like this would enable the use of a 2x3 header to convert to
the ICD connector:

x x  ICD
x x
x x
. .
. .

x .  SERIAL
. .
x .
x .
x .
o


This looks quite acceptable.


[1] http://www.ftdichip.com/Images/ttl232rsch1.jpg



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