HD44780 Hitachi Semiconductor (acquired by Renesas), HD44780 Datasheet - Page 33

• Manufacturer Part Number: HD44780
• Description: Dot Matrix Liquid Crystal Display Controller/driver
• Manufacturer: Hitachi Semiconductor (acquired by Renesas)

Interfacing to a 4-bit MPU
The HD44780U can be connected to the I/O port of a 4-bit MPU. If the I/O port has enough bits, 8-bit
data can be transferred. Otherwise, one data transfer must be made in two operations for 4-bit data. In
this case, the timing sequence becomes somewhat complex. (See Figure 17.)
See Figure 18 for an interface example to the HMCS4019R.
Note that two cycles are needed for the busy flag check as well as for the data transfer. The 4-bit
operation is selected by the program.
RS
R/W
E
Internal
operation
DB7
Note: IR7 , IR3 are the 7th and 3rd bits of the instruction.
AC3 is the 3rd bit of the address counter.
HMCS4019R
Figure 17 Example of 4-Bit Data Transfer Timing Sequence
IR7
R10 to R13
Instruction
write
Figure 18 Example of Interface to HMCS4019R
IR3
D15
D14
D13
Functioning
Busy AC3
Busy flag
check
4
RS
R/W
E
DB4 to DB7
HD44780
busy AC3
Not
Busy flag
check
COM1 to
SEG1 to
COM16
SEG40
16
40
Instruction
write
D7
LCD
D3
HD44780U
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