The following table lists the available drivers and which LCD controllers are supported by each:

CPU / Display controller interface

Different display controllers have different CPU interfaces. The most common ones are the following:

• Full bus interface
• Simple bus interface
• 4 pin SPI interface
• 3 pin SPI interface
• I2C bus interface

Full bus interface

Some LCD controllers (especially those for displays with higher resolution) require a full-address bus, which means they are connected to at least 14 address bits. In a full bus interface configuration, video memory is directly accessible by the CPU; the full-address bus is connected to the LCD controller. The only knowledge required when configuring a full bus interface is information about the address range (which will generate a CHIP-SELECT signal for the LCD controller) and whether 8- or 16-bit accesses should be used (bus-width to the LCD controller). In other words, you need to know the following:

• Base address for video memory access
• Base address for register access
• Distance between adjacent video memory locations (usually 1/2/4-byte)
• Distance between adjacent register locations (usually 1/2/4-byte)
• Type of access (8/16/32-bit) for video memory
• Type of access (8/16/32-bit) for registers

Typical block diagram for LCD controllers with full bus interface

Macros used by a full bus interface

The following table shows the used hardware access macros:

Simple bus interface

Most LCD controllers for smaller displays (usually up to 240*128 or 320*240) use a simple bus interface to connect to the CPU. With a simple bus, only one address bit (usually A0) is connected to the LCD controller. Some of these controllers are very slow, so that the hardware designer may decide to connect it to input/output (I/O) pins instead of the address bus.

Typical block diagram for LCD controllers with simple bus interface

8 (16) data bits, one address bit and 2 or 3 control lines are used to connect the CPU and one LCD controller. Four macros inform the LCD driver how to access each controller used. If the LCD controller(s) is connected directly to the address bus of the CPU, configuration is simple and usually consists of no more than one line per macro. If the LCD controller(s) is connected to I/O pins, the bus interface must be simulated, which takes about 5-10 lines of program per macro (or a function call to a rou- tine which simulates the bus interface). The signal A0 is also called C/D (Command/ Data), D/I (Data/Instruction) or RS (Register select), depending on the display controller.

The following table shows the used hardware access macros:

4 pin SPI interface

Using a 4 pin SPI interface is very similar to a simple bus interface. To connect a LCD display using 4 pin SPI interface the lines A0, CLK, DATA, and CS must be connected to the CPU.

Typical block diagram for LCD controllers with 4 pin SPI interface

Macros used by a 4 pin SPI interface

The following table shows the used hardware access macros:

3 pin SPI interface

Typical block diagram for LCD controllers with 3 pin SPI interface

Macros used by a 3 pin SPI interface

The following table shows the used hardware access macros:

I2C bus interface

Typical block diagram for LCD controllers with I2C bus interface

Macros used by a 3 pin SPI interface