LC7982A Datasheet, PDF (7/18 Pages) Sanyo Semicon Device – LCD Dot Matrix Graphics Display Controller

LC7982A
Block Functions
Registers
The LC7982A has five internal registers: the instruction register, the data input register, the data output register, the dot
register, and the mode control register.
• The instruction register holds the instruction code, which includes the start address and the cursor address. This
register is a 4-bit register, and the lower 4 bits (DB0 to DB3) of the data bus are written to this register.
• The data input register is used to temporarily hold data for external RAM, the dot register, the mode control register,
and other registers. It is an 8-bit register.
• The data output register is used to temporarily hold data read output from external RAM, and is an 8-bit register. The
cursor address passes through the data input register and is written to the cursor address counter, and when a memory
readout instruction is loaded into the instruction register, IC internal operations read from external RAM and load it
into the data output register. Data transfer to the microcontroller completes when the microcontroller reads the data
output register at the next instruction.
• The dot register holds the character pitch, the number of dots in the vertical direction, and other display data. Data
from the microcontroller passes through the data input register and is written to this register.
• The mode control register holds display state information for the LCD, such as display on/off state and the cursor
on/off/blinking state. It is a 6-bit register. Data from the microcontroller passes through the data input register and is
written to this register.
Busy Flag
This flag is set to 1 when the LC7982A is performing internal operations. In this state, the next instruction cannot be
accepted. The state of the busy flag is output from DB7 when RS is 1 and R/W is 1. The microcontroller application
software must first verify that the busy flag is 0 before writing the next instruction. However, after a data read instruction
or a data write instruction, the microcontroller may execute the next instruction without checking the busy flag after the
maximum value of the read cycle or write cycle elapses, respectively.
Dot Counter
The dot counter generates LCD display timing according to the contents of the dot register.
Refresh Address Counter
The refresh address counters control the addresses of the external RAM, the character generator ROM, and expansion
ROM. There are two refresh address counters, refresh address counter (1) and refresh address counter (2). Refresh
address counter (1) is used for the upper screen, and refresh address counters (2) is used for the lower screen. In graphics
mode, these registers output 16-bit data that is used as the external RAM address signals. In character mode, the upper 4
bits are ignored and the 4 bits of the line address counter are output in place of those four bits. These 4 bits are used as
the expansion ROM address.
Character Generator ROM
The character generator ROM holds the data for 192 characters, a total of 7360 bits. It takes a character code from
external RAM and a line code from the line address counter as its address signals, and outputs 5 bits of dot data.
Although this ROM holds a font with 192 characters, of which 160 are 5 × 7 dot characters and 32 are 5 × 11 dot
characters, up to 256 8 × 16 dot characters can be supported by using expansion ROM.
Cursor Address Counter
Instructions can be used to set up this 16-bit counter in advance. This counter holds the address when reading or writing
external RAM (either display dot data or character codes). The cursor address counter is automatically incremented after
reading or writing display data or after executing a bit set or bit clear instruction.
Cursor Signal Generator
A cursor can be displayed in character mode under instruction control. A cursor is automatically generated when the
cursor address counter and the line address counter reach the stipulated values.
Parallel to Serial Converter
Parallel data from external RAM, the character generator, or expansion RAM is converted to series data by the two
parallel to series converter circuits and output at the same time to the LCD drive circuits for the upper and lower screens
as series data.
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