Re: [lcd4linux] GPO circuitry

[Michael R. <re...@eu...>]

>>Should be no problem in hardware, but at the moment this is not 
>>supported in software. AND there's another problem: Some commands 
>>(clear, init, character define) go to _both_ displays at the same time, 
>>just by rising _both_ enable lines.

> I'm very keen to do this for myself though.  A 20x4 display is kinda small,
> and I don't like the idea of loosing software controlled backlighting with a
> 40x4 display.  Is it complicated to change those commands to address each
> display one at a time?  Or maybe make it user configurable?
> 
> I'm thinking all the commands that address both displays together are ones
> used relatively infrequently?  Consequently, addressing them one at a time
> shouldn't have a noticable performance hit?

Hmmm.... sneding data to both displays is used for icon definitions. 
This sequence is 9 bytes long, and can happen really often...

But I don't see the problem: You can use 4 control lines from the 
parallel port (AUTOFD, INIT, SELECT and STROBE). The dual-HD44780 needs 
at least three (RS, SELECT#1, SELECT#2), because you can hardwire RW to 
GND. so you have a free line to control the latch individually...


-- 
Michael Reinelt                                   Tel: +43 676 3079941
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