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Describe how to disable the DWEN fuse.

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git-svn-id: svn://svn.savannah.nongnu.org/avrdude/trunk/avrdude@651 81a1dc3b-b13d-400b-aceb-764788c761c2
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joerg_wunsch
2006-09-07 20:42:01 +00:00
parent 9579e8e77a
commit ee36ee5ab5
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doc/avrdude.texi
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@@ -1938,6 +1938,56 @@ In order to successfully program the EEPROM that way, a prior chip
erase (with the EESAVE fuse unprogrammed) is required.
This also applies to the STK500 in high-voltage programming mode.
@item
Problem: How do I turn off the @var{DWEN} fuse?
Solution: If the @var{DWEN} (debugWire enable) fuse is activated,
the @var{/RESET} pin is not functional anymore, so normal ISP
communication cannot be established.
There are two options to deactivate that fuse again: high-voltage
programming, or getting the JTAG ICE mkII talk debugWire, and
prepare the target AVR to accept normal ISP communication again.
The first option requires a programmer that is capable of high-voltage
programming (either serial or parallel, depending on the AVR device),
for example the STK500. In high-voltage programming mode, the
@var{/RESET} pin is activated initially using a 12 V pulse (thus the
name @emph{high voltage}), so the target AVR can subsequently be
reprogrammed, and the @var{DWEN} fuse can be cleared. Typically, this
operation cannot be performed while the AVR is located in the target
circuit though.
The second option requires a JTAG ICE mkII that can talk the debugWire
protocol. The ICE needs to be connected to the target using the
JTAG-to-ISP adapter, so the JTAG ICE mkII can be used as a debugWire
initiator as well as an ISP programmer. AVRDUDE will then be activated
using the @var{jtag2isp} programmer type. The initial ISP
communication attempt will fail, but AVRDUDE then tries to iniate a
debugWire reset. When successful, this will leave the target AVR in a
state where it can accept standard ISP communication. The ICE is then
signed off (which will make it signing off from the USB as well), so
AVRDUDE has to be called again afterwards. This time, standard ISP
communication can work, so the @var{DWEN} fuse can be cleared.
The pin mapping for the JTAG-to-ISP adapter is:
@table @code
@item JTAG pin
ISP pin
@item 1
@code{3}
@item 2
@code{6}
@item 3
@code{1}
@item 4
@code{2}
@item 6
@code{5}
@item 9
@code{4}
@end table
@end itemize