10 Aug
2012
10 Aug
'12
11:07 a.m.
On 10 Aug 2012 at 19:21, Fred Jan Kraan wrote:
A while ago I started deveoping something around an
Arduino like
platform to read PALs and EPROMs. See
http://fjkraan.home.xs4all.nl/comp/divcomp/ppread/. So far I developed
sketches (programs in Arduino lingo) to read out devices. I still have
to make something to analyse the output. This is trival for (EP)ROMs
and PALs without registers and tristate pins, tricky for those with...
This assuming the security fuses are blown. > > Kind regards, > Pierre
Tristate pins are easy--just add a controllable low current source to
your rig for each prospective output pin. Try to "push" the subject
pin one way or the other. If it's tristated, there is some
combination of inputs that will cause it to assert a logic state and
it will not be possible to "nudge" it--then you have not only the
knowledge that it's a tristate, but what combination of inputs cause
it to go active.
You could implement this as a single pin driving several diode-
isolated resistors.
That worked for me. Registers and internal feedback remains an
unsolved issue, however.
--Chuck