Dale Botkin >Reply-To: pic microcontroller discussion list >To: PICLIST@MITVMA.MIT.EDU >Subject: Re: [PIC]: RA4 voltage >Date: Sun, 19 Aug 2001 19:41:07 -0500 > >On Sat, 18 Aug 2001, Andy Shaw wrote: > > > Hi Folks, > > A quick question about RA4 when used for output. On most devices it is >open > > collector. What is the max voltage I can pull this up to? For example if >I > > wanted to drive a MOSFET from it could I use it to pull down to zero >volts > > and have a resistor hooked up to say a 12V supply to turn the FET on? I >have > > a feeling this is not allowed but I thought I would ask. I seem to >remember > > something in the spec for 16F87X products saying 8V or so, but I don't >have > > the spec handy and I can't get to Microchips web site at the moment! > >Data sheet says Vdd max, absolute max is Vdd + 0.6V. I have heard >otherwise secondhand, but anything higher would be out of spec. You may >need to use RA4 to drive a transistor to turn on the FET, or use a logic >level FET. > My 16f84a datasheet (DS35007a, marked Preliminary) lists Vdd + 0.3 as absolute max wrt Vss except for RA4, MCLR/ and Vdd. RA4 is listed as -0.3 to +8.5 wrt Vss. > > On the same subject what about other common logic families TTL/CMOS etc. >Do > > they have chips that take PIC level logic inputs and have open collector > > outputs that could be used in this way. Or would I be better of using >some > > sort of driver chip that is intended for the job? > >There are TTL family OC drivers. Some will withstand some relatively high >voltages, like 40V or so, I think. > The 7407 and 7417 are pretty common OC buffers. I don't think either goes quite as high as 40V. As I recall it's more like 15 or so. Others may be higher. Regards, Bob _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu