Rainbow Electronics HD44780 User Manual
Page 33
HD44780U
33
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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
IR7
IR3
Busy AC3
Not
busy AC3
D7
D3
Instruction
write
Busy flag
check
Busy flag
check
Instruction
write
Note: IR7 , IR3 are the 7th and 3rd bits of the instruction.
AC3 is the 3rd bit of the address counter.
Functioning
Figure 17 Example of 4-Bit Data Transfer Timing Sequence
D15
D14
D13
R10 to R13
RS
R/W
E
DB4 to DB7
COM1 to
COM16
SEG1 to
SEG40
4
40
16
LCD
HMCS4019R
HD44780
Figure 18 Example of Interface to HMCS4019R