The programming pin needs to accept high voltages at any time without drawing too much power for programming purposes. If it was an output then when high it would be a direct connection between +13 and +VCC, which would fry the chip. If it was low (or in the case of an open collector), then similarily it would fry itself when you tried to program it. It makes sense to turn this into a one time programmable fuse bit on OTP devices, but a flash is intended to be rewritten. The flash is so small that a bootloader is not reasonable even if it was self programming. If you want the devices built such that programming is fool proof (ie, the uC will never be in a state where programming cannot take place) then you have to live with this sort of limitiation. Of course, you could augment the die with a voltage regulator and then bring VCC to +13v to indicate programming. But then you have to live with the possibility that it'll enter programming mode with tiny voltage spikes, etc. A voltage regulator would take up a lot of die space... -Adam Jason S wrote: >This might be a bit off-topic though it does apply to the PIC10F chips. Is >there any particular reason one of the "IO" pins is input only on the >smaller chips? > >I've been working with the 12F675 a lot recently, and occasionally I need 6 >outputs and no unputs, so I have to move up to a larger chip. Even >sometimes when 5 outputs is enough, it's a nuisance to work around GPIO3 not >being usable as an output. > >Jason > >----- Original Message ----- >From: "Bob Barr" >To: >Sent: Thursday, June 10, 2004 3:06 PM >Subject: Re: [PIC:] PIC10F data sheet. > > > > >>On Thu, 10 Jun 2004 23:34:41 +0200, Jan-Erik Soderholm wrote: >> >> >> >>>Hi ! >>> >>>There is now a data sheet for the PIC10F line with a bit more then >>>the 4 pages in the first version. >>> >>>Goto MC home page and click on the "PIC10F Familiy" picture... >>> >>>The page ends with : >>> >>>"Begin your next design now. Contact your local authorized Microchip >>>distributor or corporate sales office to request PIC10F product samples" >>> >>>That "now" there sounds promising... :-) >>> >>> >>> >>A small marketing write-up on the 10F is also included in the June >>issue of the magazine 'Printed Circuit Design & Manufacturing'. No >>details but at least there's a mention of it getting out. >> >> >>Regards, Bob >> >>-- >>http://www.piclist.com hint: PICList Posts must start with ONE topic: >>[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads >> >> >> >> > >-- >http://www.piclist.com hint: PICList Posts must start with ONE topic: >[PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads > > > > > -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics