Advanced Parallel I/O - The HCS12/9S12: An Introduction to Software and Hardware Interfacing - page 325

Pin No. Symbol I/0 Function

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16

DB7
DB6
DB5
DB4
DB3
DB2
DB1
DB0
E1
R/W
RS
V EE
V SS
V CC
E2
N.C

I/0
I/0
I/0
I/0
I/0
I/0
I/0
I/0
I
I
I
—
—
—
I
—

Data bus line 7
Data bus line 6
Data bus line 5
Data bus line 4
Data bus line 3
Data bus line 2
Data bus line 1
Data bus line 0
Enable signal row 0 and 1
0 5 write to LCD, 1 5 read from LCD
0 5 instruction input, 1 5 data input
Contrast adjust
Power supply (GND)
Power supply ( 1 5 V)
Enable signal row 2 and 3

Table 7.4 ■ Pin assignment for displays with more than 80 characters

slightly more cumbersome than the memory-mapped approach due to the need to manipulate
these three signals. The HD44780U provides a set of instructions for the user to set up the LCD
parameters. The operations performed by these instructions are summarized in Table 7.5. The
meanings of certain bits in these instructions are explained in Table 7.6.
The HD44780U can be configured to control one-line, two-line, and four-line LCDs. The
mappings of the character positions on the LCD screen and the DDRAM addresses are not
sequential and are shown in Table 7.7.

7.8.1 Display Data RAM
Display data RAM (DDRAM) stores display data represented in 8-bit character codes. Its
extended capacity is 80 3 8 bits, or 80 characters. The area in DDRAM that is not used for dis-
play can be used as general data RAM. The relationships between DDRAM addresses and posi-
tions on the LCD are shown in Table 7.7.

7.8.2 Character Generator ROM (CGROM)
The character generator ROM generates 5 3 8 or 5 3 10 dot character patterns from 8-bit
character codes. It can generate 208 5 3 8 dot character patterns and 32 5 3 10 dot character
patterns.

7.8.3 Character Generator RAM (CGRAM)
The user can rewrite character patterns into the CGRAM by programming. For 5 3 8 fonts,
eight character patterns can be written, and for 5 3 10 fonts, four character patterns can be
written.