hd66421 Renesas Electronics Corporation., hd66421 Datasheet - Page 12

• Manufacturer Part Number: hd66421
• Description: Ram-provided 160 Channel 4-level Grey Scale Driver For Dot Matrix Graphics Lcd
• Manufacturer: Renesas Electronics Corporation.

MPU Interface
The HD66421 can interface directly to an MPU
through an 8-bit data bus or through an I/O port
(figure 2). The MPU can access the HD66421
internal registers independently of internal clock
timing.
The index register can be directly accessed but the
Preliminary
DB7 to
DB0
WR
RD
CS
RS
Write index
register
H8/325
Z80
Data
A15 - A0
Figure 2 8-Bit MPU Interface Examples
D0 - D7
A0 - A7
Write data
register
Figure 3 8-Bit Data Transfer Sequence
a) Interface through Bus
b) Interface through I/O Port
WR
RD
A0
C0
C1
C2
C3
Data
decoder
8
Write data
register
8
Data
12
other registers (data registers) cannot. Before
accessing a data register, its register number must
be written to the index register. Once written, the
register number is held until it is rewritten,
enabling the same register to be consecutively
accessed without having to rewrite to the register
number for each access. An example of a register
access sequence is shown in figure 3.
CS
RS
RD
WR
DB0 - DB7
CS
RS
RD
WR
DB0 - DB7
Write index
register
HD66421
HD66421
Data
Read data
register
Data
Read data
register
Data
HD66421