In SX Microcontrollers, SX/B Compiler and SX-Key Tool, DosManDan wrote:

Hey Dan, sorry to hear you haven't solved the problem yet. I read where you tried point-to-point wiring to get around the capacitance issue. I can tell you I tried the same thing, because it just makes sense, but it doesn't work. Something in the design on the board you are are using is pushing the capacitance just a little over the limit and probably causing the issue at low voltage. I know how frustrating it is to have everyone throwing suggestions and trying to run them all down.

I read your earlier posts and maybe I misunderstood, but it seemed that you were trying to program the chip with less than 5V. It's my understanding that it won't work at all like that. It has to be programmed using 5V or it pretty much will be intermitent at best. However, once programmed, it will run at less than 5V. The only way I have reliably debugged at less than 5V is with the KeyRing. You can build one, as was suggested earlier, since it is no longer sold. 

I know your board has already been designed, but if you need to redo it, there are ways to run the chip at 5V and the rest of the board at 3V and wire the inputs to accept the signals with the different voltages. Of course, it would be great if you didn't need to do this, but....

Obviously you have alot of experience designing circuits, so I hope my suggestions don't sound rediculous. I just wish I had the magic answer for you.
Dan

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