James Newton, Host piclist.com> writes: > I was browsing the site and came on this page today: > > http://www.piclist.com/techref/microchip/lcdglassdrive.htm# > > 14 I/O's, pull down sips and 4 resistors to drive a 3 1/2 digit, plus icons, > glass with no other support chips. The PIC directly drives the LCD... there > is no LCD controller. > > Since the LCD controller is the major cost in most LCDs, extending this code > to support larger matrix type LCDs could be a VERY big deal in the PIC open > source world. > > Is that still a fair statement? How big a deal is the LCD controller? You don't really need a LCD controller excepting for graphics where the video RAM must be scanned continuously. What you really need is segment drivers instead of wasting multi-purpose IO pins. Segment drivers will drive 64 and more segment lines per chip (there are separate row and column drivers and combined ones). Also using '20 mA' IO pins to drive LCD segments is a total waste of silicon. Normally segment drivers are serially addressed so a display like the one shown, if driven with segment drivers, should use no more than 6 PIC pins (including strobe and maybe contrast control via PWM). Also graphical displays have more than 2 multiplex levels and the resistor 'jungle' needed to driven them becomes huge. The segment drivers already contain this, and a common bias circuit that allows contrast setting and more. And last, large displays have threshold voltages which are out of range for normal MCUs (they need 15-28V pkpk) precisely because of the mux requirement and to maintain a reasonable contrast and speed. Peter P. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist