The HD44780 dot-matrix liquid crystal display controller and driver LSI displays alphanumeric characters and symbols. It can be configured to drive a dot-matrix liquid crystal display when interfaced with a processor. A single HD44780 can display up to one 20-character line or two 20-character lines.
3.1 Function Description
The following section introduces some of the important features of the liquid crystal display that are important for interfacing with the liquid crystal display through software.
The LCD has two 8-bit registers, an instruction register (IR) and a data register (DR).The IR stores instruction information, such as display clear and cursor shift, and address information for display data RAM (DDRAM) and character generator RAM (CGRAM). The DR temporarily stores data to be entered into DDRAM or CGRAM and temporarily stores data to be read from DDRAM or CGRAM. Data written into the DR is automatically written into DDRAM or CGRAM by an internal operation. The DR is also used for data storage when reading data from DDRAM or CGRAM. When address information is written into the IR, data is read and then stored into the DR from DDRAM or CGRAM by an internal operation.
3.1.2 Busy Flag (BF)
When the busy flag is 1, the LCD is in the internal operation mode, and the next instruction will not be accepted. When RS = 0 and R/W = 1 (Table 1), the busy flag is output to DB7. The next instruction must be written after ensuring that the busy flag is 0.
3.1.3 Address Counter (AC)
The address counter (AC) assigns addresses to both DDRAM and CGRAM. When an address of an instruction is written into the IR, the address information is sent from the IR to the AC. Selection of either DDRAM or CGRAM is also determined concurrently by the instruction.
After writing into (reading from) DDRAM or CGRAM, the AC is automatically incremented by 1 (decremented by 1). The AC contents are then output to DB0 to DB6 when RS = 0 and R/W = 1.
3.1.4 Initializing by Internal Reset Circuit
An internal reset circuit automatically initializes the LCD when the power is turned on. The busy flag (BF) is kept in the busy state until the initialization ends (BF = 1). The busy state lasts for 10 ms after VCC rises to 4.5 V
3.2 Pin assignment
The pin assignment, shown in Table1, is the industry standard for character LCD-modules with a maximum of 80 characters.