16LF876A Battery Powered System w/ICSP

[Speakerguy]

Hey,

I'm designing a PIC16LF876A board and want to use ICSP this time. The PIC is powered by a 3.7V lithium polymer battery which is connector to Vdd and then to MCLR through a 10k resistor.

I have a melabs U2 programmer. The ICSP pins I have are VPP, VDD, Data, Clock, and GND. VPP comes from the programmer and connects directly to the MCLR pin (I believe it drives a high voltage on this pin to erase the flash?). Anyway, I am desiring to know if ICSP works on an LF type PIC when it is powered by a 3.7V source or if this is entirely dependent on my programmer (I might just have to go read the melabs documentation if it is). I just wondered if anyone knew off the top of their heads if this sounded right or feasible. Thanks!

 

[eng1]

According to their documentation: "If your board is designed to run at a lower supply voltage like 3.3V and you can't safely connect 5V to the PIC, you may have issues when erasing a flash PIC. For some devices, a low-voltage erase option is available (Options > More Options in the meProg software)".

They also show a schematic with typical connection.

You might prototype and see if you can program the PIC before making the PCB.

 

[Speakerguy]

Can I put a schottky from my 3.7V battery to the VDD pin on the pic, and then connect Pin 1 of the U2 programmer connector directly to VDD pin? Thus giving me an operating voltage of 3.3V from the battery while allowing it to have 5V supply when being programmed from the U2 using ICSP?

Also I will go look at their schematic. I read the page before I checked back here and read your reply but I didn't look at the schematic I don't think unless it was the one at the bottom of the page.

 

[eng1]

You can place a jumper and run the PIC from a 5 V supply when programming, without using the Vdd pin of the programmer. All parts connected to the PIC are 5 V tolerant, right?

 

[justDIY]

huh, I thought I had a reply to this message already... anyhoo

My POV project is a small pic on a board with a shift register, and the whole thing is hard wired to a 18650 lithium cell. there is no on/off control, a button puts the pic to sleep to turn things off.

anyway, when it's time to program, I connect all the leads of my programmer, except Vdd. I haven't had any problems doing it this way. Technically it's a no no, since the target is at Vbat and the programmer is at Vusb but I just let the clamping diodes in the target pic handle the level shifting. my target is a 12F683, so it may behave differently than your larger (and considerably older) f876