[sdiy] Multiple LCD connection sanity check please

[Tom Wiltshire]

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