how do i create a negative pulse in vhdl

[Andonis]

hi there. I need to create a negative pulse in vhdl.
I am trying to activate the interrupt handling routine of the parallel port. This requires a negative pulse on one of the parralel port pins for an x number of seconds. Can anyone help me please?? thanks
antonio

 

[VhdlForLife]

If you mean by negative pulse you mean a pulse that looks like this:
---------- --------------
| |
------
then all you need to do is initialize the signal to HIGH and then set it to LOW for a short period of time and then set it HIGH again after that.
[sig][/sig]

 

[Andonis]

ummm yeah. Sorry i meant to keep the negative pulse on delay for a while. I tried loops, counters... but they are not synthesizable.. therefore useles..
does anyone know of a circuit i could do on schematic which is able to delay the pulse? thanks

 

[Guest_imported]

Hi,
Strange! What do you mean by a "counter not being synthesisable"? Counter based approach should solve your problem (if the design is synchronous).

Please elaborate if required.

Srini