[sdiy] Multiple LCD connection sanity check please

[MTG]

Bus capacitance might be an issue, but it's easily overcome with high drive 
;-)

Never overlook fewer but larger displays. In fact some of the larger ones 
are exactly as you describe (two E pins).  Plus a given user can only see 
one thing at a time.  Are you making a Solaris?

GB
www.musictechnologiesgroup.com


----- Original Message ----- 
From: "Tom Wiltshire" <tom at electricdruid.net>
To: "Neil Johnson" <neil.johnson97 at ntlworld.com>
Cc: "synthdiy diy" <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, January 11, 2011 8:19 AM
Subject: Re: [sdiy] Multiple LCD connection sanity check please


> Neil,
>
>>> I'm ok with that. Following advice I received here in the past, I've 
>>> written a buffered LCD output routine. You can stuff long messages into 
>>> a buffer, and then a background task sends a character to the LCD every 
>>> 0.5mS. The only clever bit is that you can also send delays to the LCD 
>>> buffer, which makes it easy to deal with LCD commands that take more 
>>> than a single 0.5mS time period.
>>
>> Well, if you have lots of displays then you'll presumably have lots of
>> data to display on them?  In which case 2000 bytes/s may not be fast
>> enough. In principle you can send characters to the LCD drivers in
>> sub 100us.  Some commands take longer (RETURN is typically >1ms).
>
> If we assume 2x40 displays, that's a maximum of 8x80=640 characters to 
> refresh all the screens. If I wanted a refresh rate of 20Hz, I'd need to 
> send 12800 characters per second. So you're right, I'm potentially out by 
> a factor of 6 or so. Still, I think I might wing it and see how much of a 
> problem this is. I doubt I need to refresh the whole of every screen that 
> often. Mostly I'd be updating values on one line of one or two screens.
>
> Perhaps I could shorten my background process clock some more (250us 
> instead of 500us), and then run other slower processes on every other 
> clock. That'd give me a speed boost for the LCD.
>
>> (BTW, little nitpic: capital-S stands for Siemens, the unit of
>> conductance; seconds is small-s).
>
> Didn't know that (or rather, forgot between school physics classes and 
> now). Ta!
>
> Thanks,
> Tom
>
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