Table of Contents
Advertisement
INSTRUCTIONS
General Information
When the LCD unit is controlled by an external
microprocessor, the only registers which can be
directly accessed by the microprocessor are the
instruction register (IR) and data register (DR). Con-
trol information is buffered to allow the LCD unit to
interface with various microprocessors and periph-
eral control devices with different operating speeds.
The internal operation of the LCD unit is determined
by the signals sent from the external microproces-
sor. These signals include the register select (RS)
signal, the read/write (R/W) signal, and the data bus
(DB
- DB
) signals.
0
7
Table 7 lists the instructions available to the LCD
unit, with their execution times. The instructions fall
into the following four categories.
1. Instructions for setting LCD unit functions, such
as display format and data length
2. Instructions for addressing the internal RAM's
3. Instructions for transferring data to or from the
internal RAM's
4. Other instructions
In normal operation, instructions from category
(3) are used most frequently. The internal RAM
address may be incremented or decremented auto-
matically after each data transaction, to reduce the
programming requirements of the microprocessor.
The display may also be shifted automatically after
each display data write (see Sample Instruction
Procedures section for examples). These features
facilitate the construction of efficient systems.
During the internal execution of an instruction, no
instruction other than the "busy flag/address counter
read" instruction will be accepted. During internal
operation the busy flag is set to "1". It is necessary
for the microprocessor to check that the busy flag is
reset to "0" before sending the next instruction.
NOTE
Either the microprocessor must check that the busy flag
is not set to "1" before sending each instruction, or the
interval waited before sending each instruction must be
made sufficiently longer than the execution time of the
previous instruction. For the execution time of each
instruction, see Table 7.
Display Unit User's Manual
Description of Instruction
Display Clear
RS R/W
DB
7
0
0
0
CODE
0
The display data RAM is filled with the "space"
code, 20
. The address counter is reset to zero. If
H
the display has been shifted, the original position is
restored. By execution of this instruction, the dis-
play goes off, and the cursor and character blink
functions, if activated, are moved to the upper, left-
most display position.
Display/Cursor Home
RS R/W
DB
7
0
0
0
CODE
0
= Don't Care
NOTE:
*
The address counter is reset to zero. If the dis-
play has been shifted, the original position is re-
stored. The content of the DD RAM is not affected.
The cursor and character blink functions, if acti-
vated, are moved to the upper, leftmost display
position.
Entry Mode Set
RS R/W
DB
7
CODE
0
0
0
0
I/D: The address counter is incremented (I/D = 1) or
decremented (I/D = 0) by one, following the
reading or writing of each display data RAM
character code. The cursor and character blink
functions move one display position to the right
(I/D = 1) or left (I/D = 0). The same operation
takes place when data is written to or read from
the character generator RAM.
S: When S = 1, the entire display is shifted one
position to the left (I/D = 1) or right (I/D = 0)
following the writing of a display data RAM
character code. The cursor and character blink
functions do not move relative to the display
position. When S = 0, the display is not shifted.
The display is not shifted when writing data to
the character generator RAM.
Dot-Matrix LCD Units
DB
0
0
0
0
0
0
1
DB
0
0
0
0
0
1
*
DB
0
0
0
0
0
I/D S
15
Advertisement
Table of Contents
