Custom Serial LCD Backpack

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When I first got into BASIC Stamps I was also introduced to the increasingly popular serial LCD since typical microcontrollers would lose too many pins to control a parallel interface LCD. For a parallel LCD the minimum I/O required is six (6) pins. Four (4) for the data pins in 4-bit mode, RS and EN. A serial interface uses only a single I/O pin.


The first serial LCD display I was introduced to was the SEETRON BPI-216. It was, at the time more expensive than the development boards I was buying. It operated at 2400 / 9600 bps and had a switch-selectable backlight. It also had an interesting control protocol that required the use of a preamble character. On some microcontrollers, such as the BASIC Stamp, I felt like this made the code more complex than it needed to be.

PIC-an-LCD Demo Board by Dale Wheat

Of course, I was using another serial LCD system that had a similar protocol system. The PIC-an-LCD by Dale Wheat and sold by BG Micro used an ASCII 17 or ASCII 18 to select between sending instructions or data. It had a few advantages over the SEETRON displays in that you could use practically any 2 / 4-line display and you also had a piezo speaker for audible output of the BELL character (CTRL-G) as well as four (4) general purpose outputs. I used one of these for the backlight control, giving me a software selectable backlight.

My goal was to create my own custom serial LCD backpack that would suit my own design needs. But first I thought I would mess around with design ideas using the PIC-an-LCD chip before starting my own firmware development. Messing around with design using the PIC-an-LCD allowed me to focus on layout, I/O needs and component selection / count without having to work on firmware at the same time.

The end goal (at the time) was to use the SX Microcontroller to create my own custom backpack chip. Of course, I took on a big project for my first real development using the SX MCU and that was a mistake. I spent a lot of time tripping over the learning curve for the SX while trying to create the various subroutines in assembly language. Eventually I lost interest and gave up. That and Parallax finally released their own serial LCD display and there seemed to be no point in continuing development.

If I ever revisit this in the future (highly unlikely), I will most likely use an Atmel MCU and besides the normal display functions my final plans for my own backpack was to be able to support displays with more than one EN input (such as 4 x 40) character displays, multi-tone sound output, software volume control, software backlight control (including brightness) and software contrast control.

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