Recently, our very own inimitable Max Maxfield described his experiments with Adafruit's RGB LCD shield. This reminded me of a blog I wrote for the now-defunct sister site Microcontroller Central on using these ubiquitous character-based LCD screens as write-only memories.
This all brings back memories of the late 1970s, when I discovered the character-based displays from Hitachi. I still remember the thrill of finding the ICL7660, a switched-capacitor, negative voltage generator that provided an easy and cheap way to generate the -5 V necessary to adjust the viewing angle of the LCD. (All-5V technology was still a dream back then.)
The LCD module was a harbinger of the direction electronic packaging would take later as it moved to surface mount technology. Now I have been working with these character-based LCD displays for more than 30 years. About 10 years ago, I was even motivated to write a Circuit Cellar article (subscription required) on a systematic way to create hierarchical menus for displays based on a 20x4 LCD character module. When I read Max's blog, I decided it was time to drag out my soapbox again.
Having observed many failure modes over the years, I have become concerned with designing robust systems. I want to reduce the probability of problems occurring and ensure the system can recover gracefully if (when) they occur.
The Hitachi HD44780 dot-matrix LCD driver is nothing more than a dedicated microcontroller. It's subject to the same vagaries as any other microcontroller. Power supply surges, long cables, alpha particle radiation, and other things that go bump in the night can all scramble its operation.
Failure on the display is a much higher-profile event, since it is the first thing the user sees, even if the rest of the system is operating correctly. Failure to design for this possibility means the whole system must be reset to re-initialize the display.
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