On Thu, 16 Apr 2009 18:30:46 -0400, "Olin Lathrop" said: > > You guys seem to forget that these are level shifter circuits, not > > microcontrollers. The cap is there simply to keep the voltage on > > RS232 from going too far below 10V, for the duration of the bit. > > It's a digital circuit that has switching transients and two or three > charge > pumps. Unless the datasheet explicity says otherwise, the assumption > should > be that good power supply bypass is required. The fact that they > explicitly > call for 1uF should be a big clue that something there matters more than > usual. I'm going with Vitaliy here. The 1uF requirement is for bulk capacitance, not low ESR. Any cap will work perfectly fine. The resistance in the switching elements is higher than the ESR of the worst electrolytic. Cheerful regards, Bob -- http://www.fastmail.fm - mmm... Fastmail... -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist