HD66724 Datasheet, PDF (35/117 Pages) Hitachi Semiconductor – (Graphics LCD Controller/Driver with Key Scan Function)

HD66724/HD66725
a. When unused character patterns are not programmed: If an unused character code is written into
DDRAM, all its dots are lit, because the EPROM is filled with 1s after it is erased.
b. When unused character patterns are programmed as 0s: Nothing is displayed even if unused
character codes are written into DDRAM. (This is equivalent to a space.)
Instructions
Outline
Only the instruction register (IR) and the data register (DR) of the HD66724/HD66725 can be controlled by
the MPU. Before starting internal operation of the HD66724/HD66725, control information is temporarily
stored in these registers to allow interfacing with various peripheral control devices or MPUs which operate
at different speeds. The internal operation of the HD66724/HD66725 is determined by signals sent from the
MPU. These signals, which include the register selection signal (RS), the read/write signal (R/W), and the
data bus signal (DB0 to DB7), make up the HD66724/HD66725 instructions. There are five categories of
instructions that:
• Control the display
• Control power management
• Set internal RAM addresses
• Transfer data with the internal RAM
• Control key scan (when serial interface mode)
Normally, instructions that perform data transfer with the internal RAM are used the most. However, auto-
incrementation by 1 (or auto-decrementation by 1) of internal HD66724/HD66725 RAM addresses after
each data write can lighten the MPU program load.
Because instructions other than clear display instruction are executed in 0 cycle, instructions can be written
in succeccion.
While the clear display instruction is being executed for internal operation, or during reset, no instruction
other than the key scan read instruction can be executed.
35