Post by thread:[PIC]: ICSP on 16F628 and MCLR

I'm new to pics and need some help on a project I'm working on. Can I do ICSP on a 16F628 if MCLR is internally tied to Vdd? Or does it matter when programming? Any help would be greatly appreciated. -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

On Thu, Jul 11, 2002 at 02:03:17PM -0500, Richard Mellina wrote: >I'm new to pics and need some help on a project I'm working on. Can I do > ICSP on a 16F628 if MCLR is internally tied to Vdd? Yes. From my testing if MCLR is defined as internal, then power cycling Vdd is the mechanism for causing an ordinary reset. > Or does it matter when programming? The programming cycle is unchanged. For high voltage programming (HVP), the trigger has always been Vpp on MCLR rising to 3.5V above Vdd. For low voltage programming, the programming pin is attached to RB4 which must be grounded for ordinary operation. In neither case will programming mode be entered usless explictly triggered, in which case programming mode is entered as normal. >Any help would be greatly appreciated. > The bottom line is that you can treat the PIC16F628 as normal even when MCLR is set to internal. However you've missed the real problem which I'd like to put on the table: If one is using a HVP ICSP programmer and has MCLR set to internal, then how does one use the input for ordinary uses when 13V will be dropped on the line when programming? Short of using it for a switch, or interfacing a transistor/diode, how can one connect ordinary logic to the pin? It's currently an intellectual exercise with me because I'm only doing LVP at the current time. But I was wondering... BAJ -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> However you've missed the real problem which I'd > like to put on the table: If one is using a HVP ICSP programmer and has > MCLR set to internal, then how does one use the input for ordinary uses > when 13V will be dropped on the line when programming? Short of using it > for a switch, or interfacing a transistor/diode, how can one connect ordinary > logic to the pin? Usually you don't. I've done this with a diode and a pulldown resistor. ***************************************************************** Embed Inc, embedded system specialists in Littleton Massachusetts (978) 742-9014, http://www.embedinc.com -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

> I'm new to pics and need some help on a project I'm working on. Can I do > ICSP on a 16F628 if MCLR is internally tied to Vdd? Or does it matter when > programming? Any help would be greatly appreciated. ICSP works even if the "MCLR" pin is defined to be a normal I/O pin. Bob Ammerman RAm Systems -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

----- Original Message ----- From: "Bob Ammerman" <spam_OUTrammermanTakeThisOuTADELPHIA.NET> To: <.....PICLISTKILLspam@spam@MITVMA.MIT.EDU> Sent: Thursday, July 11, 2002 3:15 PM Subject: Re: [PIC]: ICSP on 16F628 and MCLR > > I'm new to pics and need some help on a project I'm working on. > Can I do > > ICSP on a 16F628 if MCLR is internally tied to Vdd? Or does it matter when > > programming? Any help would be greatly appreciated. > > ICSP works even if the "MCLR" pin is defined to be a normal I/O pin. > > Bob Ammerman > RAm Systems MCLR may be defined for other uses if you don't need a hardware reset at run time, however.. If MCLR is tied directly to VDD, raising it to VPP will raise VDD to about 13 volts across the board. This could be bad for the PIC, and any other chips that happen to be sharing the (usually +5Volt) VDD line. It could also require more current than many simpler programmers can provide. Unless I misunderstand the question?? Lyle Hazelwood -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads

>The bottom line is that you can treat the PIC16F628 as >normal even when MCLR is set to internal. However you've >missed the real problem which I'd like to put on the >table: If one is using a HVP ICSP programmer and has MCLR >set to internal, then how does one use the input for >ordinary uses when 13V will be dropped on the line when >programming? Short of using it for a switch, or interfacing >a transistor/diode, how can one connect ordinary logic to the pin? >It's currently an intellectual exercise with me because I'm >only doing LVP at the current time. But I was wondering... This sounds rather like a case of you loose a pin either way :) MCLR if you HVP, or RB4 if you LVP. :(( -- 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

On Fri, Jul 12, 2002 at 08:29:51AM +0100, Alan B. Pearce wrote: > >The bottom line is that you can treat the PIC16F628 as > >normal even when MCLR is set to internal. However you've > >missed the real problem which I'd like to put on the > >table: If one is using a HVP ICSP programmer and has MCLR > >set to internal, then how does one use the input for > >ordinary uses when 13V will be dropped on the line when > >programming? Short of using it for a switch, or interfacing > >a transistor/diode, how can one connect ordinary logic to the pin? > > >It's currently an intellectual exercise with me because I'm > >only doing LVP at the current time. But I was wondering... > > This sounds rather like a case of you loose a pin either way :) > > MCLR if you HVP, or RB4 if you LVP. :(( Quite true, at least in the ICSP scenario. Of course if the you use the internal RC oscillator, you can convert the two OSC pins into general purpose I/O pins. BAJ -- 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