program in circuit at 3.3V??

nicenoise · Joined: 10 May 2004 Posts: 17 Location: barcelona

hello,
is it possible to program in circuit at 3.3V VCC??
there is an alert message in the ICD when i try...
i'm working with PIC18F1330 and some componentes at 3.3V,
this is a problem because i have to change de voltage supply to 5V and put out the other componentes in program mode...

any sugestions?

thanks a lot,

alex

Ttelmah · Guest

Look at section 19.9 of the data sheet.
Only the Vpp pin has to go above the supply.
These chips don't support low voltage ICSP. They support ICSP, with MCLR taken to Vpp.
I you want to use low voltage ICSP, you have picked the wrong chip.

Best Wishes

jgd10 · Joined: 21 Jul 2008 Posts: 8 Location: Fresno

I have the same question. This is my first circuit, so bear with me.

My circuit is 3.3v and I want to use the Mach X to program it. The FAQ "How do I connect the Mach X Programmer to my own hardware" states that a +5v from target circuit must be sent to Mach X, but my circuit is only 3.3v.

Does anyone know if I can use the 3.3v instead of the posted 5v?

The FAQ is at:
http://www.ccsinfo.com/faq.php?page=machx_connection

Any help would be appreciated.

ljbeng · Joined: 10 Feb 2004 Posts: 205

I have 5v and 3.3v on my board. The 5 volt only powers the ICD when it is connected. The 3.3V powers all other chips on the board. I don't do anything special, I just connect 5v, MCLR, B7, B6 and Ground to the ICD and debug and serial program with no problems.

jgd10 · Joined: 21 Jul 2008 Posts: 8 Location: Fresno

Thanks. I'm building my first pcb and I wanted to get this right. I'm sure I'll have to build it again, but I at least want to get this part right for debugging purposes.

RLScott · Joined: 10 Jul 2007 Posts: 465

The fact that ICSP must take place at +5v means that you must design your board so that anything attached to the Vdd of the PIC must be capable of withstanding the +5v that will be applied during programming. If you have a circuit that is connected to Vdd and can't take the temporary +5v, then perhaps you should design in a jumper that can be removed during programming to disconnect anything that can't take it.
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Robert Scott
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Embedded Systems Consulting

jgd10 · Joined: 21 Jul 2008 Posts: 8 Location: Fresno

Thanks Robert, I'll make of this.

Guest · Posted: Wed Jul 30, 2008 9:33 am

The ICD-U40 programs 18LF6722 fine with VCC at 3.3v
We've programed several thousand boards with it like that.
Everything runs from 3.3v, you get the warning message but they still program.

Jim