Phillip wrote:

>Hi
>I've been following all this programming thread with some interest.
>I have a lot of designs that operate at 3V but it hurts none of my
>components to let the programmer take the supply to 5V.
>I have to operate at 3V for of a couple of reasons.
>1)In some configurations I "steal" power from the antenna voltage GPS
>receivers send to their antenna so 3V consumes less power 2)some receivers
>though still quite rare only supply 3V to start with.
>(Actually it is always just a hair above 3V because the antenna preamplifier
>operates at 3V then you need to send a little more to over come the I^2R
>losses so to make a long story short an LDO reg will give you 3V no
>problemo)
>  
>
I know what you are doing. I did a cellular modem / GPS anklet for 
criminals.

>  
>Now I have a future product where the firmware will be wildly complex but it
>will not "steal" power.....if it did it would quickly drain all available
>power from all but the most high end/robust GPS receivers. 
>To say that I'm going to nail the code on the first release or not want to
>change this or that for some of my customers in the first few revisions is
>wish full thinking at best and stoopid at worst.
>  
>
If you can release errorless code, Uncle Sam could use a guy like you, 
because at the very
least, you can walk on water. Ever rolled dice in Vegas? I'd buy the 
plane ticket...

All kidding aside.. NOBODY does that. If somebody tells you that 
somebody did that, you
better reach around and make sure you still have your wallet, cause if 
he'll lie about that,
he's apt to do ANYTHING.

>My quantities are fairly low and testing will be very complex.
>So I have no problem with adding the header for the ICSP but I can't expect
>my customers in the field to have handy dandy ICSP or to open the box to
>connect to it plus when these are fielded they are some times
>installed/mounted in the rafters with a man lift and I use a blue tooth
>serial link to control the thing.
>
>  
>
What I would do is use a 5-pin spring-loaded probe array to install 
minimal firmware, like a
"bootloader". Then program it through the normal bluetooth serial 
channel. I have done
two designs like this and they work very well. AND they both ran at 
3.3V. These were both
PIC16F88, not nearly as powerful as the PIC18F6520.

To solve the need to update the firmware almost entirely, I stored the 
new firmware in a
32K I2C EEPROM until all had been received, then went on an "updating 
binge" for 2-3
minutes until everything was installed (nothing else could operate 
during the binge). Another
advantage about the storage scheme is that it allows you to perform a 
CRC of the data.
The data stored is NOT in hex, it is in actual data; that way the 
compiler outputs data is not
a factor.

>I wanted to leave my basic designs at 3V if I could because the RF portion
>works fine there no need to reinvent the wheel etc. 
>So is the lesson I need to take away from all this is that in order to
>realistically be able to alter my code in the field via a serial port I will
>need to operate the PIC at 5V???
>  
>
No, if you are using the bootloader scheme, it is 3V just like standard 
operation. It just
might take a few mS longer to program each batch of new data (the F88 
installs 16 words
at a time). No 5V is needed when doing internal updates, unless you need 
to change the
configuration word. BTW, My scheme could install internal EEROM data as 
well, by simply
writing it like normal operation.

>(Right now I'm using a 18F6520 or it I might go larger if it turns out I
>need more I/O or use a second device.
>
>
>I'd love to hear any of the groups thoughts and advice....thanks in advance
>for any replies.
>  
>
I have a lot of experience with this, be glad to give some advice... if 
not too much, I will
do it for free. NOTE: when updating firmware make SURE the packet is 
thoroughly vetted
(protected from error during transfer), cause firmware data has to be 
bulletproof.

--Bob

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