How to extend a pulse width without clock!

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Due to a chip bug, I have to extend a pulse width(negative)from 10ns
to 100ms in CPLD(Altera 7128). But the difficult is that I have no any
clock into the CPLD, so the CPLD is pure combination logic. how to
extend it in such case?

Help me!

Re: How to extend a pulse width without clock!
Am not sure you can.. all the logic on the chip can't generate that kind of
delay..  but you might find another signal which you can use as a clock A0
if you have a micro.. or ALE.. WR.. RD something like that.. failing that..
an RC off chip :-)

Simon


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Re: How to extend a pulse width without clock!
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uups, bad luck - not recommended but if you have enough free pins and logic
you and if the timing is not critical it is possible to make free running
oscillator without external RC components, just connect uneven count of
inverters in ring (ie 3 inverters) as this is astable it will oscillate
with pretty high frequency, this could be divided down, but from about
40MHz down to 100ms its pretty long counter ... and this approuch
really isnt 'recommended'

as other options build simple RC on IO cells and use that signal

antti

Re: How to extend a pulse width without clock!

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Can you add some very small components? You can build a very simple
monostable by connecting a RC network between two CPLD pins.

--
Lorenzo



Re: How to extend a pulse width without clock!



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I have delayed strobe signals several hundred nS with an external series
resistor, and used the input capacitance of the chip as the C of the RC
network.  For mS, you will need an external capacitor, of course.  if you
want the delay to be asymmetric (like a one-shot), you might need to
put a diode in parallel with the R.  You feed the signal out one pin,
through a series R, to a pin loaded with a cap to ground, and then take
the signal in from that pin.  This may cause multiple pulses with a
delay this long, however.  So, you might end up using a 74HC4538
or similar one shot, or a 74HC14 Schmitt trigger to prevent the
pulses as the output of the RC crosses the threshold.

Jon


Re: How to extend a pulse width without clock!
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The board is in production, so I can not change the SCH and PCB, all
things should be done in CPLD.

Peter

Re: How to extend a pulse width without clock!
You could take two cascaded flip-flops, feed the first with '1' and use your
10 ns strobe as async reset for both. Take a 100 ms (10 Hz) clock or clock
enable signal for the FFs and combine both outputs to a 100 ms strobe.

Regards,
Stephan Flock



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