in circuit programming

icp_pic · Joined: 09 Jan 2008 Posts: 4

hi all,

i am working on several projects that require in circuit programming. when using the icd-u40 (like all icd's) it occupies some of the pins i would like to dedicate to my projects. i know i read about this some where, but can't find my notes on it. there was an ic designed to allow you to use the pins for programming and then use those same pins for your project when the programmer is detached or not in use.

there maybe a wide selection of these chips on the market to date. if i could just get a name, web site, or a company i could google it. i tried to google what i thought it might be called, but the long searches continuously turn up null. has there been any projects here that used such a technique that i can be privy to...?

the bootloader technique seems to be of interest too, but again you have to use dedicated pins or do you. let me know. i would like information on both. hopefully the same ic can be used to address both techniques: icd-u40 and bootloader.

the users hear seemed to be very knowledgeable and keen. i was wondering if i could get this question addressed or pointed in the right direction. any suggestion (good or bad) are welcome. i just want to get the wheels turning and solve this (if possible). thank you in advance to all who respond.

Guest_7068 · Guest

Almost all the PIC chips (18F452, 16F877 for example) have the pins B6 and B7 multiplexed with the ICSP programming clock and data pins. These 2 pins and all other pins on port B are labeled as 'Digital I/O' according to the data sheet. Once the programmer is disconnected, you should be able to perform I/O on these pins.

icp_pic · Joined: 09 Jan 2008 Posts: 4

hmm.. interesting, 1 of my projects is on the 16f876. ill check the data sheet. im not sure if the i/o's are as you say on the 16877, but these 2 chips are extremely similar according to the data sheet. ill have a look.

my other project that is giving me trouble is on a 12f509 which may or may not have this feature. ill do a another google search on multiplex ics and see what i get. thanks again for the suggestion.

newguy · Joined: 24 Jun 2004 Posts: 1907

It's not necessary to 'reserve' the ICSP pins just for programming - they can be used normally. The only thing you have to watch for is what circuitry is connected to those pins. I don't know the specifics as to what a programmer will tolerate, but I've run into problems with my programmer not recognizing or not properly programming PICs if I use the PIC's programming pins. Some peripherals are okay (LCDs), but others cause problems. I install shorting pins & 2 pin headers on those lines to isolate everything from the PIC so that I don't have programming problems.

icp_pic · Joined: 09 Jan 2008 Posts: 4

thanks newguy, that is exactly what i have been doing - using headers, but thats what i am trying to avoid on the revision of these projects to make them less of a hassle to program. im trying to get close to making one connection which is the programmer and let the internal circuit do the rest.

i recall reading something about a ic that would act like the headers for you when you need to program and vice versa when you wanted to use the on board components. i dont remember where i saw it tho.. Crying or Very sad

Humberto · Posted: Thu Jan 10, 2008 7:59 am

For most applications, a 10K resistor is enough to isolate RB7 & RB6 pins without degrading
the programming signals. The ICSP must be tied directly to those pins (PGD / PGC).
Of course, it is not applicable to ALL the needs, but always there is the choice to reserve
these pins as inputs to share them in this way without the need of any jumpers/IC.

Humberto