Mecanique's internal bootloader OSC

[SUNFLOWER]

Yes did that, and it did work once, tantalizingly close to crystal freedom.

[Charles Linquis]

We have some boards that are too small for an additional MAX232 chip. We bring out the Tx and Rx pins anyway (along with Vcc and GND). When programming is needed, we plug in a board that has a MAX232 chip and a DB9 connector on it.

So we can have a bootloader AND a small, low-cost board.

The real upside is that having a serial port is one of the best debugging tools around.

The boards start up at 4Mhz, but the code "downshifts" to 1Mhz for power savings. It is a tiny temperature sensor, and any dissipation shows up as a temperature error. The chips are 18F2321s and run on the internal oscillator only.

[SUNFLOWER]

Yes Bruce I was going down that road eliminating the MAX232 until I considered the advantages of loader-free possibilities with boots. Firmware updates will be all over the map, some in the most remote areas of India. And they are religious about not spending money. So I thought eliminating loaders, like U2, would be a good trade-off for using the MAX232 (and I really like hardware serial functions HSEROUT/HSERIN). I did read Mecanique worries about internal oscillation drift, so maybe if we want to eliminate programming hardware we should just work with crystals, totally not needed for tracking a slow moving sun. Will defer until the industry matures and PICs operating crystal-free can be reliably bootloaded. It is amazing how much stuff is unexpected.

It would be great if PICs also had internal voltage regulators and internal MAX232. Maybe someday.

Thanks,
Doug

[SUNFLOWER]

Good ideas, Charles, I will consider that type of connection. So you bootload with internal oscillation, what ambient temperatures, and do you experience bootloader reliability issues?

Being user-friendly is very important. I agree that the serial port is useful. Olimex makes a PIC carrier board with the all the needed peripherals for (I hope) less than $10 at scale.

[Charles Linquis]

We have chamber-tested random units at -40C and 100C, about 30 units total.

Never any failures.

I assure you, you won't have any trouble at any temperatures humans would want to be at for any length of time.

About 90% of what we do is military. Reliability is important to them, too.

[SUNFLOWER]

OK good Charles, that settles it. Now to solve that software problem of setting one OSCCON bit in bootleg.hex... I will let the forum know when I hear back from Mecanique.

Hacking Tiny boot was a good idea. Maybe pointing was absolute someplace and did not like inserts, or the program stepped on its tail, or something.

Best,
Doug