[sdiy] Multiple LCD connection sanity check please

[Neil Johnson]

Hi Tom,

> If I were connecting several LCDs to a single microprocessor, would I be able to do the following?:
>
> Tie all the LCD R/W pins to 'Write' (I'm not interested in reading from the displays). This will put the data pins into Hi-Z mode and let me..
> ..Parallel all the LCD data ports together (I'm using an 8-bit interface).
> Use the individual 'Enable' pins on each display to select which LCD responds to messages sent to the display bus

Tricky.

Reading the HD44780U controller datasheet I see there are 125uA (typ)
pullups on the Data lines (equivalent to around 40k).  If you have
lots of displays in parallel then your drivers must be able to
comfortably pull down a few mA quickly.

It also means you won't be polling the BUSY flag then?  In that case
you will have to make assumptions about execution time of LCD commands
and hope you're not wrong, or take conservative estimates and suffer
the performance penalty.

How many displays are you intending of paralleling up?

Cheers,
Neil
-- 
http://www.njohnson.co.uk