Thanks for all the suggestions for this problem. I looked through the ISD site's application notes & there is one about interfacing to 5V micro's. It says that the ISD4000 series can accept 5V no problem but the ISD5008 data sheet says in the specs that voltage on ANY input is Vcc + 0.3V max! I emailed ISD & Bruce Jordan replied very promptly with; Quote Yep, the ISD5008 will accept 5 volt logic signals without difficulty. You still need to do the same thing as for the ISD4000 with the MISO line, though. Sorry it is not clear from the Data Sheet; I will see what we can do for the next revision. Unquote Isn't it nice to get questions answered from semi manufacturers ?! Regards... At 09:14 5/18/00 +0300, you wrote: >On 18 May 00, at 15:22, David Duffy wrote: > > > At 11:55 5/17/00 +0100, you wrote: > > >In-Reply-To: <4.3.1.2.20000517171853.00a79180@192.168.0.100> > > > > > >David Duffy wrote: > > > > Hi All, > > > > This is my 1st time using 3v3 devices (ISD5008 voice chip) and was > > > > wondering about the best way to interface the PIC to it. (5v supply) > > > > Brian Gregory wrote; > > >Use an open drain output type idea. > > > > > >When you have an output from the PIC (5V) to the voice chip (3V) put a > > >pull up resistor to 3V and instead of driving the output high for logic > > >one just set it to high impedance with the TRIS register. > > >The other way round an output from the voice chip into a PIC input > > >should work as is because the PIC will take 3V as logic one anyway. > > > > Hmmm... Seems like a good idea but... > > Does the PIC input being held at 3V (near 5V mid-point) pose a problem? > > If it's not a schmitt trigger input, I thought CMOS inputs are unhappy > > about this. > > Regards... > > It's the best ideea, I don't know how I forgot ... PIC will see as >high level anything up to ~1,8V...2V . > And a CMOS have thresolds at 1/3 and 2/3 from VDD so 2/3 from >5V is 3.3V that's the reason why CMOS are unhappy when is >supplied at 5V and interfaced with a signal coming from a 3.3V >circuit... and not because of schmitt trigger inputs... >But a good (standard) CMOS chip will work either at 3V (with >frequency limitation ) so no problem... >Vasile