ICP via optocouplers?

[Norbert]

Anyone with experience of ICP of 18F... (or 16F...) via optocouplers?
I need electrical isolation for safety reasons between the PIC circuit and a permanently-connected-PC-with-Internet.
Can use LVP or an onboard source of higher voltage for MCLR pin.
I realize this is not a hardware forum, but it is the kind of place where someone might have tried something like this...

Tips, suggestions etc. appreciated!

[HenrikOlsson]

Never tried, don't know if it's straight forward or tricky as hell (since the PGD-pin is bi-directional for example) but if I were to try it I'd probably try with one of ADUM series digital isolators or something like that.

But what's the application? Why is there a permanently connected PC to the programming port of the PIC?
Is it perhaps possible to initially program the PIC with a bootloader and then, instead of trying to isolate the ICSP pins, use an isolated RS232 connection to the PC? That way you have isolated serial AND programming at the same time.

/Henrik.

[towlerg]

between the PIC circuit and a permanently-connected-PC-with-Internet

I don't understand why you want to use ICSP (which I assume is what you meant). Surley it would be easier to use either USB and RS232, which could both be connected via optocouplers. Your optocouplers would have to be real fast to use USB 2.0

Sorry in advance if I've misunderstood.

George

[pedja089]

There is somewhere documentation for this
http://www.microchipdirect.com/produ...words=AC244005
So you can take a look how they did that.
But I also don't understand why you need this...
EDIT: http://ww1.microchip.com/downloads/e.../50002085B.pdf
Page 130-133

[Dave]

Why not just use a bootLoader? That way you can update the firmware via. the rs232 connection.

[Norbert]

Thanks for all the replies, apologies for the late response.
Yes, it would make a lot more sense to use a bootloader, and although I will take a look at the adapter described in the link sent by Pedja089, it is probably not certified for the 10kV isolation that the application demands.

The application is for an existing piece of hardware built around a 18F67K22 - production changes to the hardware itself would be expensive.
That's why I was considering using an external optocoupler-based adapter and connecting it permanently to the ICSP port on the existing hardware.

The problem with using a bootloader is that there is no remotely-accessible reset function on the existing hardware. If it were a new design, I could use an output pin from the MCU to drive a one-shot pulse circuit which would pull down the MCLR pin causing a reboot and the option of entering the bootloader via the existing (already optoisolated to 10kV!) RS485 port (goes to the USART of the MCU). Are the any pre-coded bootloaders for this MCU that can be accessed from the main (PBP) code - i.e. post-boot, WITHOUT a reset button? Suggestions on how to do a reboot without reset button, and without pulling MCLR low? Maybe by using the WDT and with a USART command calling a timeout?

[Norbert]

... and for the curious:

The application is existing PIC-based hardware used for environmental monitoring in grain storage silos.
Because of the potentially explosive atmosphere, there are strict requirements on the hardware used. Thus the opto-isolation on all ports to the "outside world".
The hardware is already in use in several places around the world, including places where it would be very expensive to go to do a firmware update on site. But because of new items of associated hardware, changes to the code in the controller MCU are occasionally needed.