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The `dongle' shown here (dongle.gif) was designed by Ken Huntington
(kenh@compmore.net). It is perhaps unique in not `protecting' a
copyright, being perfectly transparent to the sp12 software - so you
can still use a plain cable with this version. And the dongle has no
power requirements; the 74HC126 receives its Vcc from the port. Yet
it significantly improves the signal quality. The Sck termination
(as shown in progrmmr.pdf and icp_intr.pdf) becomes superfluous when
using it. Some parallel ports won't reliably communicate with an AVR
uC without it. Moreover, the programming lines are high-Z except
when sp12 is active.

Apart from powering the dongle, your parallel port will also still
be able to provide power for a small target board (Icc up to about
5 mA). When using external power, the high-Z lines make the order of
switch-on and connection less critical. You can switch on the target
board first and then connect it to the PC, or make the connection
and switch it on afterwards. But do make sure that your board resets
properly! The absolute minimal `reset circuit' is a resistor of
about 10K between Vcc and the uC's reset pin.

A pcb layout for the dongle can be found on the sp12 Web page:

   http://www.xs4all.nl/~sbolt/e-spider_prog.html

There are also photo's of our prototypes. A 74HC126 is preferred,
but the dongle does seem to work well enough with a 74HCT126, if the
parallel port provides a reasonable Vcc value.