This question is derived from this Board review thread, I thought it would be preferable to make it a standalone question.
I want to be able to reset a PIC remotely using the only communication port of the board, the RS232. But I also want to be able to program it using a ICD3 (no bootloader), and this programmer apparently applies high voltage (0-13V?) to /MCLR which will certainly kill the MAX232 (MAX233 in fact).
Would a schottky between R2out of the MAX233 and 5V be the way to go? The datasheet says that the absolute maximum voltage on that pin is 5.3V, I find it a bit tight for a schottky. Any more robust suggestions? I don't want to use a jumper as this could be forgotten...
Will this work?
The Zener is a ON SEMI BZX84B5V1LT1G that has 5-5.2V tolerance at 5mA and I'm allowing 4.4mA max. The MAX233 will drive the /MCLR pin at 0.41V where up to 1V is a low level. The 20kOhm pull up comes from one of Olin's answers here.