Microprocessor Interface
The LCD unit performs either dual 4-bit or single
8-bit data transers, allowing the user to interface with
either a 4-bit or 8-bit microprocessor
4-Bit Microprocessor Interface.
Data lines DB
4
- DB
7
are used for data transfers.
Data transactions with the external microprocessor
take place in two 4-bit data transfer operations.
The high-order 4 bits (corresponding to DB
4
- DB
7
in an 8-bit transfer) are transferred first, followed by
the low-order 4 bits (corresponding to DB
0
- DB
3
in
an 8-bit transfer). The busy flag is to be checked on
completion of the second 4-bit data transfer. Busy
flag and address counter are output in two opera-
tions.
8-bit Microprocessor Interface
Each 8-bit piece of data is transferred in a single opera-
tion using the entire data bus DB
0
- DB
7
.
IR
7
DB
7
DB
6
DB
5
DB
4
RS
R/W
E
IR
3
AC
3
DR
7
DR
3
BF
IR
6
IR
2
AC
2
DR
6
DR
2
AC
6
IR
5
IR
1
AC
1
DR
5
DR
1
AC
5
IR
4
IR
0
AC
0
DR
4
DR
0
AC
4
Write to
Instruction
Register (IR)
Read Busy
Flag (BF) and
Address
Counter (AC)
Read Data
Register (DR)
LCD27-9
Figure 2. 4-Bit Data Transfer
Dot-Matrix LCD Units
Display Unit User’s Manual 11
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