Why exactly do you need a LCD controller board to interface LCD to a microcontroller?

Question

I've dealt with interfacing a very simple LCD display with a microcontroller, so I get the basic concepts. I'm trying to interface something a bit more involved.

I'm a bit confused on why you would need a LCD controller board to interface a LCD that displays nothing more than simple characters (no graphics). Take this LCD from Electronic Assembly for example. It has a table of command for the LCD controller SSD1803. Does this mean I cannot interface this LCD screen without a lcd controller board to my microcontroller?

Answer 1

You don't need an external controller for this kind of LCD. This is the controller.

In general, character LCD modules will include the controller, usually with some variation of the Hitachi HD44780 controller, perhaps with a different data interface than the ancient 4/8 bit interface.

Graphic LCD modules, especially color ones, tend to need an external controller with a frame memory. In some cases that may be part of your MCU or FPGA so it can share memory and respond quickly, in other cases there may be a controller as part of the module so it can work with a much more modest micro (at a cost in complexity, dollars and speed). In the former case, the interface is sort of a digital version of a video signal- color digital values refreshed regularly at some frame rate. The pixel rate will be beyond the ability of a small micro to handle even if it did nothing else.

Answer 2

The LCD module that you're referencing includes the SSD1803 controller. You do not need an additional controller.

Generally speaking, direct LCD interfaces have a number of features that make them difficult to work with:

• They are analog interfaces, and often require unusual operating voltages.
• They involve a lot of pins (typically, one for every row and every column for monochrome displays).
• They must be switched at somewhat high frequencies for correct operation.
• They do not inherently provide any graphical rendering features (such as alphanumeric characters).

Combined, these features make it impractical to interface directly with an LCD. Instead, most small LCDs are packaged with a controller which drives the LCD and presents a more "friendly" digital interface. In this case, that controller uses a parallel interface compatible with the HD44780; in other small displays, SPI and I2C interfaces are not uncommon. Larger LCDs tend to use different interfaces, such as MIPI, LVDS, DVI/HDMI, or DisplayPort.

Answer 3

I'm a bit confused on why you would need a LCD controller board to interface a LCD that displays nothing more than simple characters (no graphics).

The controller boards you see are normally backpacks that provide additional features. The basic ones allow you to control the LCD from a serial/uart or a i2c/SPI connection. The goal is to save pins or memory. A direct HD44780 connection will need between 7 to 12 pins. The backpack may only need 2 or 3. It may also allow for animations or automatic controls.

You can definitely connect directly to that LCD, but a controller middleman may help save time, money and effort.