HARDWARE
Interface Signals
Functional Blocks
Registers
The LCD unit has two 8-bit registers - an instruc-
tion register (IR) and a data register (DR). The
instruction register stores instruction codes such as
"clear display" or "shift cursor", and also stores
address information for the display data RAM and
character generator RAM. The IR can be accessed
by the microprocessor only for writing.
The data register is used for temporarily storing
data during data transactions with the microproces-
sor. When writing data to the LCD unit, the data is
initially stored in the data register, and is then auto-
matically written into either the display data RAM or
character generator RAM, as determined by the
current operation. The data register is also used as
a temporary storage area when reading data from
the display data RAM or character generator RAM.
When address information is written into the instruc-
tion register, the corresponding data from the display
data RAM or character generator RAM is moved to
the data register. Data transfer is completed when
the microprocessor reads the contents of the data
register by the next instruction. After the transfer is
completed, data from the next address position of
the appropriate RAM is moved to the data register,
in preparation for subsequent reading operations by
the microprocessor. One of the two registers is
selected by the register select (RS) signal.
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Table 2. Interface Signals
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Table 3. Register Selection
Dot-Matrix LCD Units
4
Display Unit User’s Manual
