Hardware Reference
In-Depth Information
Symbol
Meaning
Min.
Typ.
Max.
Unit
t
CYCLE
Enable cycle time
1000
-
-
ns
PW
EH
Enable pulse width (high level)
450
-
-
ns
t
Er
,
t
Ef
Enable rise and decay time
-
-
25
ns
t
AS
Address setup time, RS, R/W, E
60
-
-
ns
t
DDR
Data delay time
-
-
360
ns
t
DSW
Data setup time
195
-
-
ns
t
H
Data hold time (write)
10
-
-
ns
t
DHR
Data hold time (read)
5
-
-
ns
t
AH
Address hold time
20
-
-
ns
Table 7.10
■
HD44780U bus timing parameters (1-MHz operation)
Symbol
Meaning
Min.
Typ.
Max.
Unit
t
CYCLE
Enable cycle time
500
-
-
ns
PW
EH
Enable pulse width (high level)
230
-
-
ns
t
Er
,
t
Ef
Enable rise and decay time
-
-
20
ns
t
AS
Address setup time, RS, R/W, E
40
-
-
ns
t
DDR
Data delay time
-
-
160
ns
t
DSW
Data setup time
80
-
-
ns
t
H
Data hold time (write)
10
-
-
ns
t
DHR
Data hold time (read)
5
-
-
ns
t
AH
Address hold time
10
-
-
ns
Table 7.11
■
HD44780U bus timing parameters (2-MHz operation)
Example 7.4
▼
Write a set of LCD routines that perform the following functions for the Dragon12 demo board:
1.
cmd2LCD (char cmd)
. This function sends the command
cmd
to the LCD kit.
2.
openLCD (void)
. This function initializes the LCD.
3.
putcLCD (char cx)
. This function outputs the character
cx
to the LCD kit.
4.
putsLCD (char *ptr)
. This function outputs a NULL-terminated string pointed to by
ptr
to
the LCD kit.
Solution:
The procedure for sending a command to the IR of the LCD is as follows:
Step 1
Pull the RS and the E signals to low.
Step 2
Pull the R/W signal to low.
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