Post by thread:[PIC:] How critical are the Vdd/Vpp sequencing whe

I have noticed that the datasheets for various PICs indicate a specific sequence of moving Vdd up slightly and then raising Vpp from Vdd to high voltage, then programming the chip, then cycling back down. Yet, in the DIY programmer schematics I've seen, it looks like they're getting away with just turning on Vdd and leaving it at +5V without changing it at all, and just turning Vpp from 0V to +13V in one step. So how picky are the PICs really about following the programming specs in this respect? Should I expect that building a simple programmer which just turns on/off Vdd and Vpp (at high voltage) would be sufficient? How important is it for Vpp to sit at +5V (as opposed to 0) when not in program mode? (I'm assuming it should stay at +5V or +13V, but as long as I'm asking questions, I'll toss that one in too). Thanks, steve -- Steve Willoughby | "It is our choices... that show what we truly <spam_OUTsteveTakeThisOuTalchemy.com> | are, far more than our abilities." | --Albus Dumbledore, in Harry Potter and the | Chamber of Secrets, by J. K. Rowling -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

hmm. I've noticed that one sure-fire way to figure out something on your own is to walk over and ask someone else, only to have the answer finally dawn on you (maybe just by going through the exercise of framing the question differently to ask someone else)... I think I just did that to myself in my previous question posted here, although I wish I had that epiphany BEFORE I hit "send". Okay, so I think I was mentally confusing the PIC with another chip (an EPROM) I'm also working with which had different timing requirements for program mode. So feel free to just ignore my previous question, unless the following still doesn't sound right... I ought to be able to hold the chip at 0V (all pins), then raise Vpp and Vdd (in the order specified by the chip's datasheet) from 0V to their program voltages, then clock the data in. In general, random I/O pins may be floating, at Vdd, Vpp, or Vss during programming and verification. (Since on multi-chip programmers they need to appear on several different pins.) Fiddling with Vdd at different levels is only for verification, and I'm guessing isn't always strictly necessary for prototypes and hobby work. Sound right? --steve -- Steve Willoughby | "It is our choices... that show what we truly <steveKILLspamalchemy.com> | are, far more than our abilities." | --Albus Dumbledore, in Harry Potter and the | Chamber of Secrets, by J. K. Rowling -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

Yes. Steve Willoughby wrote: {Quote hidden}>hmm. > >I've noticed that one sure-fire way to figure out something on your >own is to walk over and ask someone else, only to have the answer >finally dawn on you (maybe just by going through the exercise of >framing the question differently to ask someone else)... I think >I just did that to myself in my previous question posted here, >although I wish I had that epiphany BEFORE I hit "send". > >Okay, so I think I was mentally confusing the PIC with another >chip (an EPROM) I'm also working with which had different timing >requirements for program mode. > >So feel free to just ignore my previous question, unless the >following still doesn't sound right... > >I ought to be able to hold the chip at 0V (all pins), then raise >Vpp and Vdd (in the order specified by the chip's datasheet) >from 0V to their program voltages, then clock the data in. > >In general, random I/O pins may be floating, at Vdd, Vpp, or Vss >during programming and verification. (Since on multi-chip >programmers they need to appear on several different pins.) > >Fiddling with Vdd at different levels is only for verification, >and I'm guessing isn't always strictly necessary for prototypes >and hobby work. > >Sound right? >--steve >-- >Steve Willoughby | "It is our choices... that show what we truly ><EraseMEstevespam_OUTTakeThisOuTalchemy.com> | are, far more than our abilities." > | --Albus Dumbledore, in Harry Potter and the > | Chamber of Secrets, by J. K. Rowling > >-- >http://www.piclist.com#nomail Going offline? Don't AutoReply us! >email listservspam_OUTmitvma.mit.edu with SET PICList DIGEST in the body > > -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email @spam@listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

> Should I expect that building a simple > programmer which just turns on/off Vdd and Vpp (at high voltage) > would be sufficient? It will work for most parts. It will fail on most parts that can configure /MCLR as input pin *if the code in the chip actually does so*. It might even fail on some chips without doing this, but IIRC I have not seen this yet. Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email KILLspamlistservKILLspammitvma.mit.edu with SET PICList DIGEST in the body