At 04:40 PM 3/26/2010, James Newton wrote: >Dwayne, thanks for pointing out that 8, 14 and 20 pin chips can >interchange... I assume some of the 18 pin chips can as well... very >interesting... now if I can just connect the more commonly used components >to the IO pins that will still be there if a smaller PIC is installed... >ahh.. .more complexity in the design, I just love it. So far as I know, none of the 18 pin PICs are pin-compatible with the 8/14/20 pin parts. I can send to you a copy of the layout that I use for the 14 pin parts. Its pretty useful - pins RA0, 1, 2, 4, 5 and all 6 port RC pins are brought out to a simple but extremely flexible configuration area. This area allows each pin to be configured as input or output with a variety of pull-up and pull-down networks. Pin RA3 is dedicated for power-up reset on these layouts - I rarely need all of the pins anyway when I'm prototyping. The block includes a 78L05 or LP2950A TO-92 regulator with input & output bypass caps and a J175 FET used for power-up reset (usable only if Vunreg is above 11Vdc). The pull-up on MCLR is a fairly low value so that Vdd gets completely drained to 0vdc when power is removed. The input options for each available pin include: pull-up to Vdd or Vunreg, pull-down to Gnd plus a separately configurable voltage divider with optional zener clamp or filter capacitor. Obviously, there can be a series resistor on the pin if desired. The output options for each available pin include: series resistor, TO-92 digital NPN (DTC143ES) open-collector output driver (B-C-E pinout) with optional pull-up resistor to Vunreg, TO-92 digital PNP open-collector output driver (E-B-C pinout) with optional pull-down to GND. You can substitute MOSFETs in place of the transistors mentioned above but you may have to bend the pins around. Note that the "digital transistors" I mention above are transistors with an integrated series resistor on the base plus shunt resistor between B-E and are intended for use in logic circuits. Rohm, NEC, others make them. All of that in an area of 1.5" x 1.2". Its intended to use all through-hole parts but I've been known to glom SMD resistors and capacitors down in various places when it was convenient to do so. Its easier to show it than it is to describe. I've just block-copied that part of the layout from one of my board layouts but the smallest I've been able to make it is about 75K. I'll send a copy to James and anyone else who asks for it rather than dump another unwanted 75K file into everybody's mailbox. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax www.trinity-electronics.com Custom Electronics Design and Manufacturing -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist