Post by thread:[PIC] LVP, bulk erase and potential problems (and

Hi. Now, if I have understood things correctly, there is a potential problem during bulk erase with the LVP feature. A bulk erase will reset the LVP bit and enable LVP. If the programmer then releases the target PIC from programming mode (by lowering the prog voltage on MCLR), there is a risk that the processor will enter LVP mode (if the PGM pin isn't pulled down with a resistor. And (still if I've understood correctly), this is not a problem if the programmer keeps the MCLR pin at Vpp over the whole erase to fuse re-programming cycle (?). And also that a pulldown on the PGM pin will always protect against this scenario ? The reason I ask is that the Wisp628 has a LVP connection/cable. I've never connected it to anything myself, and it's not perfectly clear from Wouters Wisp628 page *when* it should be used. I'd like to understand the LVP issues fully to be able to better support my local Wisp628 customers in Sweden. On a local Swedish electronics forum, there was a statement today saying that failing to handle the PGM pin correctly can brake a 16F628A. Comments ? Best Regards, Jan-Erik.

{Quote hidden}>-----Original Message----- >From: spam_OUTpiclist-bouncesTakeThisOuTmit.edu [.....piclist-bouncesKILLspam@spam@mit.edu] >Sent: 29 November 2005 13:23 >To: piclistKILLspammit.edu >Subject: [PIC] LVP, bulk erase and potential problems (and a >littleWisp628...) > > >Hi. >Now, if I have understood things correctly, there is >a potential problem during bulk erase with the LVP >feature. A bulk erase will reset the LVP bit and enable >LVP. If the programmer then releases the target PIC >from programming mode (by lowering the prog >voltage on MCLR), there is a risk that the >processor will enter LVP mode (if the PGM pin >isn't pulled down with a resistor. > >And (still if I've understood correctly), this is >not a problem if the programmer keeps the MCLR >pin at Vpp over the whole erase to fuse re-programming >cycle (?). > >And also that a pulldown on the PGM pin will >always protect against this scenario ? > >The reason I ask is that the Wisp628 has a >LVP connection/cable. I've never connected >it to anything myself, and it's not perfectly clear >from Wouters Wisp628 page *when* it should >be used. I'd like to understand the LVP issues >fully to be able to better support my local >Wisp628 customers in Sweden. > >On a local Swedish electronics forum, there was a >statement today saying that failing to handle the PGM >pin correctly can brake a 16F628A. Comments ? > >Best Regards, >Jan-Erik. Putting a pulldown on the PGM pin should prevent any programming issues. The only time LVP has ever given me grief was when it was accidently left floating. Regards Mike ======================================================================= This e-mail is intended for the person it is addressed to only. The information contained in it may be confidential and/or protected by law. If you are not the intended recipient of this message, you must not make any use of this information, or copy or show it to any person. Please contact us immediately to tell us that you have received this e-mail, and return the original to us. Any use, forwarding, printing or copying of this message is strictly prohibited. No part of this message can be considered a request for goods or services. =======================================================================

Jan-Erik Soderholm wrote: > And (still if I've understood correctly), this is > not a problem if the programmer keeps the MCLR > pin at Vpp over the whole erase to fuse re-programming > cycle (?). Yes, if it can. Note that Vpp is often required to go to 0 between some operations, like bulk erase and programming data. > And also that a pulldown on the PGM pin will > always protect against this scenario ? Yes. > On a local Swedish electronics forum, there was a > statement today saying that failing to handle the PGM > pin correctly can brake a 16F628A. Maybe, but I would need to see solid evidence for me to believe that. ****************************************************************** Embed Inc, Littleton Massachusetts, (978) 742-9014. #1 PIC consultant in 2004 program year. http://www.embedinc.com/products

[yes! a PIC topic!] > The reason I ask is that the Wisp628 has a > LVP connection/cable. I've never connected > it to anything myself, and it's not perfectly clear > from Wouters Wisp628 page *when* it should > be used. I don't realy know when it could be *unconnected* so I always connect it to the PGM pin (that is, if the chip has one). > On a local Swedish electronics forum, there was a > statement today saying that failing to handle the PGM > pin correctly can brake a 16F628A. Comments ? break the chip? I would be surprised! Wouter van Ooijen -- ------------------------------------------- Van Ooijen Technische Informatica: http://www.voti.nl consultancy, development, PICmicro products docent Hogeschool van Utrecht: http://www.voti.nl/hvu