Em 28/04/2014 09:36, Larry Bradley escreveu:
> An LCD display connected to a PIC requires a minimum of 6 port pins.
> With small pin-count PICs, this can be a problem.
>
> Many years ago, when the Basic Stamp came out, some clever chap provided
> a serial LCD display - it used RS232 - to reduce the pin count (this was
> in the days of the 16F84).
>
> I want to do the same thing but using SPI. (I just want it for myself -
> I don't plan on producing anything). I can always get a chip with SPI
> hardware to use as the LCD driver, but I though I would try it with a
> couple of chips I have on hand, using software SPI.
>
> I've done SPI master in software - no problem. It seems to me that doing
> the slave shouldn't be difficult at all - it is really a very simple
> system. I've search the Internet to see if there are any software slave
> implementations out there, but no luck. Rather than re-invent the wheel,
> do any of you know of any?


How about using a simple shift-register (74HC/HCT595) for the slave?

In the simplest implementation you will use three pins (SCK, SDO, LOAD).
It can be simplified to two pins if you use an RC timer for the LOAD pin
(that is what is used in PPM R/C (remote-control) receivers).

Isaac

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