It's a good chance that the Adafruit display supports readback. In my experience with this type of display, they are almost always HD44780 types (even if they use a"newer" chip made by a different vendor).
In my day job, I work on products that need to be very reliable. A few years ago, I was assigned to qualify some new LCD displays because the driver IC had changed. I discovered that in some of our older products the new displays had a tendency to go blank when zapped with ESD. The vendor was able to fix the problem with better shielding and a different IC but it would have saved a lot of trouble if the firmware guys back then had used a periodic readback to check the health of the display...
I often see discussions of the most popular computer architecture- 8 bits/16 and 32 bits, but I don't ever recall seeing ann passion being expended on 4 bit devices. My bet would be for the HD44780 just based on the time it has been available and the sheer number of displays that have been produced.
Depends. If the display is for an LCR meter (for example) then yes, if it does not work the operator can just power it off and on. But if it is used in a piece of medical equipment, or a critical process control application, then these techniques are very good to know. Thanks as always for an informative article.
I recently got some BIIIIG vacuum fluorescent 4 x 20 character displays which I described in my recent article here. I thought they'd be standard HD44780 types - NOT! Very strange things - most control codes were actually input as text but in the 00h-20h range (much like the old printers). They DID have a control line but it was only used for a couple of things - resetting the display for example. But they are lovely displays. Useful for impressing Veeps, amongst other things :-)
@Antedeluvian: Thanks for this blog -- I must admit that I'd never thought of doing this, by which I mean reading back from the display to make sure it was up and running (or in your case just monitoring the BF signal).
I'm not sure if my Adafruit display supports reading back -- I'll have to check -- but I'll certainly incorporate some tests based on your blog into any future equipment I design involving displays.