LCD display control is used for controlling the driving of dot matrix LCD displays. This controller belongs to the computer I/O device interface, controlled by MPU, and operates the LCD display driver to achieve various display functions on dot matrix LCD display devices.

Its use frees MPU from tedious display control, making dot matrix LCD display devices more suitable for intelligent systems. The characteristics of the controller can be summarized as follows:

① Having a simple MPU interface, the controller presents the general characteristics of a parallel interface to the MPU.

② It has a complete set of logic control circuits and timing generators, which can manage the display buffer and control various functions.

③ Equipped with a fully functional control finger set, the MPU can easily control the display function of the controller itself and even the liquid crystal display device through programming.

④ It has the ability to transmit display data and transmit timing pulse signals, and can directly control the LCD display driver.

In terms of structure, LCD display control can be divided into three components: interface section, control section, and output section.

(1) Interface Department

The interface unit is used to receive instructions and data from the MPU and provide feedback on the required data information to the MPU. The interface unit has two channel ports, one is the instruction channel port; The other is the data channel port. The instruction channel port is used to receive and temporarily store instruction codes sent by the MPU, waiting for the internal logic circuit of the controller to decode and implement the corresponding functions. This channel is also connected to the 'busy' flag register. The symbol 'busy' indicates the current operational status within the controller. MPU can retrieve the "busy" flag by reading the instruction channel to determine when to operate the controller. The data channel port is used to receive and send display data. MPU can access the display buffer through the data channel port, and the controller's instructions are often supplemented with parameters, such as setting the cursor address pointer. After setting the instruction, the input of the two byte address parameter should be followed immediately. These parameters also need to be transmitted to the corresponding parameter registers through the data channel port, and the instruction code at this time is like a register selection code to select various parameter registers.

(2) Control Department

LCD display controllers have the ability to independently process information. The LCD display control unit is the implementation circuit of this capability.

Equipped with independent timing oscillators and logic control circuits, it enables the management of display buffer RAM and the setting of character generators; Realize the generation of various timing pulse signals for liquid crystal display drivers, and combine the data of different display buffers according to certain states of parameter registers in a certain pattern, and then send them out to achieve various display effects.

Any display device requires the establishment of a display buffer, and liquid crystal display devices are no exception. In order to not occupy the memory resources of the MPU, the LCD display controller has the ability to manage RAM. Due to the size of the display buffer changing with the display screen, the display buffer is generally not integrated inside the controller but connected to the controller in the form of peripheral circuits. Therefore, in addition to power supply and certain hardware settings, the control pins mainly manage the display buffer, generally having 16 bit address output lines, 8-bit data lines, and read/write control output lines.

(3) Drive Department

The driver is the interface between the controller and the LCD display module. It provides the required frame scanning signals, row and column shift pulses, row and column latch pulses, column display data signals, and driver AC driving waveform signals to the drivers in the LCD display module. The driving unit sends the display data to the display hybrid circuit under the addressing of the refresh address pointer, and converts it into serial display data format output in the parallel/serial circuit. The output pulse timing is generated by a timing generator. The LCD display module has requirements for the configuration of control sequence, and the controller is not suitable for various drivers. Therefore, the driving circuit form used in the LCD display module limits the controller, which is mainly reflected in the certain requirements for the data output mode of the control driving part.

(4) Instruction set

The controller has a set of dedicated instructions for the MPU to operate it. Instruction sets can generally be divided into three categories.

① System work settings category

This type of instruction is used to set the system's working mode, display buffer partitioning, etc.

② Display mode setting class

This type of instruction includes display status, display mode, display synthesis, and cursor display settings.

③ Data operation category

This type of instruction includes address pointer setting, address pointer change direction setting, and read/write operation commands.