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'[PIC] Switching to 3V'
2009\06\14@154149 by solarwind

picon face
I ordered some 3 V chips yesterday - the PIC32MX440F512 as well as
some dsPIC33 3.0 - 3.6 V chips.

1. I have a pickit2 and will be using it to power and program the
target. Question: will the pickit2 work with these 3.3 V chips or will
it zap them 5 V?

2. I'll be using a MAX233A to interface the PICs with a PC via UART.
It converts RS232 levels to 5V levels. How do I make the 5V levels
into 3 V levels so I don't fry my PICs?

-- [ solarwind ] -- http://solar-blogg.blogspot.com/

2009\06\14@164200 by Jan-Erik Soderholm

face picon face
solarwind wrote:
> I ordered some 3 V chips yesterday - the PIC32MX440F512 as well as
> some dsPIC33 3.0 - 3.6 V chips.
>
> 1. I have a pickit2 and will be using it to power and program the
> target. Question: will the pickit2 work with these 3.3 V chips or will
> it zap them 5 V?

It would surprice me *a lot* if the docs doesn't answer that.

>
> 2. I'll be using a MAX233A to interface the PICs with a PC via UART.
> It converts RS232 levels to 5V levels. How do I make the 5V levels
> into 3 V levels so I don't fry my PICs?

Use the 3.3V version of the MAX232, of course...

2009\06\14@164330 by Isaac Marino Bavaresco

flavicon
face
solarwind escreveu:
> I ordered some 3 V chips yesterday - the PIC32MX440F512 as well as
> some dsPIC33 3.0 - 3.6 V chips.
>
> 1. I have a pickit2 and will be using it to power and program the
> target. Question: will the pickit2 work with these 3.3 V chips or will
> it zap them 5 V?
>
> 2. I'll be using a MAX233A to interface the PICs with a PC via UART.
>  

Didn't you mean MAX232?

> It converts RS232 levels to 5V levels. How do I make the 5V levels
> into 3 V levels so I don't fry my PICs?

Use the MAX3232, it is a 3.3V part.
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2009\06\14@165321 by solarwind

picon face
On Sun, Jun 14, 2009 at 9:43 PM, Isaac Marino
Bavaresco<spam_OUTisaacbavarescoTakeThisOuTspamyahoo.com.br> wrote:
> Didn't you mean MAX232?

No. I meant MAX233A.

> Use the MAX3232, it is a 3.3V part.

Good idea, I'll sample a 3.3 V transceiver.

2009\06\14@165414 by Bob Blick

face
flavicon
face
solarwind wrote:
> I ordered some 3 V chips yesterday - the PIC32MX440F512 as well as
> some dsPIC33 3.0 - 3.6 V chips.
>
> 1. I have a pickit2 and will be using it to power and program the
> target. Question: will the pickit2 work with these 3.3 V chips or will
> it zap them 5 V?

There are some cases of the low voltage chips being killed by glitches
from the PicKit2. Olin's LProg programmer is specifically for the low
voltage parts and can't damage them because it only does low voltage parts.

> 2. I'll be using a MAX233A to interface the PICs with a PC via UART.
> It converts RS232 levels to 5V levels. How do I make the 5V levels
> into 3 V levels so I don't fry my PICs?

The MAX233A is only spec'ed down to 4.5V so in order to use it you'd
have to power it from a separate supply and it'd be a real kludge. Using
a MAX3232 is the usual cure, that way everything runs on 3.3v.


Cheers,

Bob

2009\06\14@195110 by Xiaofan Chen

face picon face
On Mon, Jun 15, 2009 at 4:54 AM, Bob Blick<.....bobblickKILLspamspam@spam@ftml.net> wrote:
> There are some cases of the low voltage chips being killed by glitches
> from the PicKit2. Olin's LProg programmer is specifically for the low
> voltage parts and can't damage them because it only does low voltage parts.

Unless you are not following the PICKit 2 user guide, you should not
be able to destroy the 3V3 chips by using PICKit 2. I am using PICkit
2 now with PIC24F USB PICs and it works very well.


--
Xiaofan http://mcuee.blogspot.com

2009\06\14@201325 by olin piclist

face picon face
Xiaofan Chen wrote:
>> There are some cases of the low voltage chips being killed by glitches
>> from the PicKit2. Olin's LProg programmer is specifically for the low
>> voltage parts and can't damage them because it only does low voltage
>> parts.
>
> Unless you are not following the PICKit 2 user guide, you should not
> be able to destroy the 3V3 chips by using PICKit 2. I am using PICkit
> 2 now with PIC24F USB PICs and it works very well.

This has nothing to do with the PICKit 2.  I know you think it cures cancer,
slices veggies, and performs foot massages, but geesh, you could give it a
rest every now and then.

I expect that if you follow the directions exactly for other programmers,
they also won't destroy 3.3V devices.  My USBProg for example won't zap a
3.3V part if you follow the directions and always tell it what chip is out
there.  If you don't, it will try to read the device ID and decide from
that.  And yes, of course it starts with the lowest voltage algorithms and
works its way up, and most of the time that will work just fine.  The
problem is that if there is any communications glitch, it might not read the
device ID and therefore proceed thru algorithms which include 5V Vdd and 13V
Vpp.

This seems like a basic issue that all multi-voltage programmers, including
the PICKit 2, are faced with.  That's one of the reasons behind the LProg,
the other being cost.  It only puts out 0-3.3V and therefore can't fry 3.3V
parts, costs less than the PICKit 2, and also works correctly over the full
range of valid USB power voltages.


********************************************************************
Embed Inc, Littleton Massachusetts, http://www.embedinc.com/products
(978) 742-9014.  Gold level PIC consultants since 2000.

2009\06\14@204554 by Vitaliy

flavicon
face
solarwind wrote:
>I ordered some 3 V chips yesterday - the PIC32MX440F512 as well as
> some dsPIC33 3.0 - 3.6 V chips.
>
> 1. I have a pickit2 and will be using it to power and program the
> target. Question: will the pickit2 work with these 3.3 V chips or will
> it zap them 5 V?

I used Pickit2 briefly with a 33F, it worked fine. YMMV.


> 2. I'll be using a MAX233A to interface the PICs with a PC via UART.
> It converts RS232 levels to 5V levels. How do I make the 5V levels
> into 3 V levels so I don't fry my PICs?

Both PIC32 and dsPIC33 have 5V tolerant pins.

So one way to make it work, is to power the PIC from 3.3V, and power the MAX
from 5V. The logic HIGH threshold for MAX233 is 2V, which means you can
connect the UART output (tx) pin directly to it (with a pullup resistor to
3.3V). Select a 5V tolerant pin for UART input (rx), and you're set.

Vitaliy

2009\06\14@215340 by solarwind

picon face
On Mon, Jun 15, 2009 at 1:44 AM, Vitaliy<spamspamKILLspammaksimov.org> wrote:
> I used Pickit2 briefly with a 33F, it worked fine. YMMV.

Perfect!

> Both PIC32 and dsPIC33 have 5V tolerant pins.

Oh snap! That's just what I need!

> So one way to make it work, is to power the PIC from 3.3V, and power the MAX
> from 5V.

Yep, I'm planning to put a 3.3 V linear regulator from the PICKIT2 V+
pin to the pin on the PIC.

> The logic HIGH threshold for MAX233 is 2V, which means you can
> connect the UART output (tx) pin directly to it (with a pullup resistor to
> 3.3V). Select a 5V tolerant pin for UART input (rx), and you're set.

That's perfect, thanks!

2009\06\14@223456 by Funny NYPD

picon face
No, it shouldn't.
PICkit 2 has its own Vdd generation circuits and On/Off control circuits. For more detail on understanding PICKit 2 hardware, please refer to this tutorial:
http://augroups.blogspot.com/2009/05/understanding-microchip-pickit-2-rev.html

Funny N.
Au Group Electronics, http://www.AuElectronics.com




________________________________
From: Xiaofan Chen <.....xiaofancKILLspamspam.....gmail.com>
To: Microcontroller discussion list - Public. <EraseMEpiclistspam_OUTspamTakeThisOuTmit.edu>
Sent: Sunday, June 14, 2009 7:51:08 PM
Subject: Re: [PIC] Switching to 3V

On Mon, Jun 15, 2009 at 4:54 AM, Bob Blick<bobblickspamspam_OUTftml.net> wrote:
> There are some cases of the low voltage chips being killed by glitches
> from the PicKit2. Olin's LProg programmer is specifically for the low
> voltage parts and can't damage them because it only does low voltage parts.

Unless you are not following the PICKit 2 user guide, you should not
be able to destroy the 3V3 chips by using PICKit 2. I am using PICkit
2 now with PIC24F USB PICs and it works very well.


--
Xiaofan http://mcuee.blogspot.com

2009\06\14@225054 by Vitaliy

flavicon
face
Vitaliy wrote:
> The logic HIGH threshold for MAX233 is 2V, which means you can
> connect the UART output (tx) pin directly to it (with a pullup resistor to
> 3.3V).

This doesn't make sense.

The pullup resistor is not needed if you just need to drive the output to
+3.3V (Vdd). The only reason to use a pull-up, is if you want to drive the
output above the supply voltage (e.g., to +5V) by using a pin in open drain
configuration.

Vitaliy

2009\06\14@230430 by Xiaofan Chen

face picon face
On Mon, Jun 15, 2009 at 8:13 AM, Olin Lathrop<@spam@olin_piclistKILLspamspamembedinc.com> wrote:
> This has nothing to do with the PICKit 2.  I know you think it cures cancer,
> slices veggies, and performs foot massages, but geesh, you could give it a
> rest every now and then.

You said this too many times. I do not hold such believe though. It is you
who hold this believe. Anyway, I do not care about your non-technical
rants.

> This seems like a basic issue that all multi-voltage programmers, including
> the PICKit 2, are faced with.  That's one of the reasons behind the LProg,
> the other being cost.  It only puts out 0-3.3V and therefore can't fry 3.3V
> parts, costs less than the PICKit 2, and also works correctly over the full
> range of valid USB power voltages.

This makes sense. So LProg does make some sense.


--
Xiaofan http://mcuee.blogspot.com

2009\06\15@005101 by solarwind

picon face
>> Both PIC32 and dsPIC33 have 5V tolerant pins.

Update: the DSPIC 33 FJ 128 GP 802 page
(http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en532298)
says that "All digital input pins are 5V tolerant". Aren't all of the
pins enabled for digital input? So can I just plug it into the socket
I have for my 18F2620 and start working with it right away? (both 28
pin, so I assume same pinout)

2009\06\15@045201 by Jan-Erik Soderholm

face picon face
solarwind wrote:
>>> Both PIC32 and dsPIC33 have 5V tolerant pins.
>
> Update: the DSPIC 33 FJ 128 GP 802 page
> (http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en532298)
> says that "All digital input pins are 5V tolerant". Aren't all of the
> pins enabled for digital input?

No, *you* enable a pin for digital input. I have not checked, but
this might say that a pin enabled for analog input (the default?)
is not 5V tolerant...

> So can I just plug it into the socket
> I have for my 18F2620 and start working with it right away? (both 28
> pin, so I assume same pinout)

Why on earth are you assuming that ??

2009\06\15@050515 by Tamas Rudnai

face picon face
On Mon, Jun 15, 2009 at 1:13 AM, Olin Lathrop <KILLspamolin_piclistKILLspamspamembedinc.com>wrote:

> This has nothing to do with the PICKit 2.  I know you think it cures
> cancer,
> slices veggies, and performs foot massages, but geesh, you could give it a
> rest every now and then.
>

The only pitfall I have heard about PICkit2 is that when you have a 5V
device selected first and then you just plug a 3.3V one, there could be a
very short period of time when the PIC still gets 5V till the programmer
recognises the device. I think that's even mentioned in the programmer's
manual and also how to avoid that. It may happen with other programmers as
well with automatic device selection.

Tamas
--
http://www.mcuhobby.com

2009\06\15@074051 by Isaac Marino Bavaresco

flavicon
face
solarwind escreveu:
>>> Both PIC32 and dsPIC33 have 5V tolerant pins.
>>>      
>
> Update: the DSPIC 33 FJ 128 GP 802 page
> (http://www.microchip.com/wwwproducts/Devices.aspx?dDocName=en532298)
> says that "All digital input pins are 5V tolerant". Aren't all of the
> pins enabled for digital input? So can I just plug it into the socket
> I have for my 18F2620 and start working with it right away? (both 28
> pin, so I assume same pinout)
>  

They mean: All pins that are purely digital, it is, don't have analog
capabilities. The A/D inputs, A/D reference inputs and comparator inputs
aren't 5V tolerant.


Regards,

Isaac

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2009\06\15@122847 by solarwind

picon face
On Mon, Jun 15, 2009 at 12:40 PM, Isaac Marino
Bavaresco<RemoveMEisaacbavarescoTakeThisOuTspamyahoo.com.br> wrote:
> They mean: All pins that are purely digital, it is, don't have analog
> capabilities. The A/D inputs, A/D reference inputs and comparator inputs
> aren't 5V tolerant.

Ya, I checked the datasheet, only 8 pins on the device are 5V
tolerant. And pinout is similar, but not identical to the PIC18F2620.

2009\06\15@141154 by Vitaliy

flavicon
face
solarwind wrote:
>> They mean: All pins that are purely digital, it is, don't have analog
>> capabilities. The A/D inputs, A/D reference inputs and comparator inputs
>> aren't 5V tolerant.
>
> Ya, I checked the datasheet, only 8 pins on the device are 5V
> tolerant. And pinout is similar, but not identical to the PIC18F2620.

If you need more 5V tolerant pins, use voltage dividers for inputs, and
transistors for outputs.

Vitaliy

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