Command Set - Xilinx Spartan-3A User Manual

Chapter 5: Character LCD Screen
The CG RAM address counter either remains constant after read or write operations, or
auto-increments or auto-decrements by one location, as defined by the I/D set by the
Mode Set
Figure 5-5
character is stored in the fourth CG RAM character location, which is displayed when a
DD RAM location is 0x03. To write the custom character, the CG RAM address is first
initialized using the
the custom character location. The lower three address bits point to the row address for the
character bitmap. The
character bitmap row. A '1' lights a bit on the display. A '0' leaves the bit unlit. Only the
lower five data bits are used; the upper three data bits are don't care positions. The eighth
row of bitmap data is usually left as all zeros to accommodate the cursor.

Command Set

Table 5-2
the display is set up for four-bit operation, each eight-bit command is sent as two four-bit
nibbles. The upper nibble is transferred first, followed by the lower nibble.
Table 5-2: LCD Character Display Command Set (4-bit mode)
Function
Clear Display
Return Cursor Home
Entry Mode Set
Display On/Off
Cursor and Display Shift
48
command.
provides an example that creates a special checkerboard character. The custom
Set CG RAM Address
Write Data to CG RAM or DD RAM
A5 A4 A3 A2
Character Address Row Address
0 1 1 0
0 1 1 0
0 1 1 0
0 1 1 0
0 1 1 1
0 1 1 1
0 1 1 1
0 1 1 1
Figure 5-5: Example Custom Checkerboard Character with Character Code 0x03
summarizes the available LCD controller commands and bit definitions. Because
0
0
0
0
0
www.xilinx.com
command. The upper three address bits point to
Upper Nibble
Write Data to CG RAM or DD RAM
A1 A0 D7 D6 D5
Don't Care
0 0 - - -
0 1 - - -
1 0 - - -
1 1 - - -
0 0 - - -
0 1 - - -
1 0 - - -
1 1 - - -
Upper Nibble
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
0 0 0 0
Spartan-3A/3AN Starter Kit Board User Guide
command is used to write each
Lower Nibble
D4 D3 D2 D1
Character Bitmap
0 1 0 1
1 0 1 0
0 1 0 1
1 0 1 0
0 1 0 1
1 0 1 0
0 1 0 1
0 0 0 0
Lower Nibble
0 0 0 0
0 0 0 1
0 0 1 I/D
0 1 D C
1 S/C R/L -
UG334 (v1.0) May 28, 2007
R
Entry
D0
0
1
0
1
0
1
0
0
1
-
S
B
-