1Semiconductor
FEDL9090A-01
ML9090A-01, -02
Serial Interface Operation
1. Start byte
A register that transfers instruction codes (including display data or key scan data) is selected by a content of the
start byte (see below).
D7
D6
D5
D4
D3
D2
D1
D0
“1”
“1”
RS
R/W
Register number
(1) D7, D6 (fixed at “1”)
When selecting the start byte register, always write a “1” to bits D7 and D6.
(2) D4 (R/W) (Read mode, Write mode select bit)
1: Read mode is selected
0: Write mode is selected
(3) D5, D3 to D0 (Register number)
The correspondence between each content of the start byte and each register or the display data RAM is listed in
the table below.
D7
D6
D5
D4
D3
D2
D1
D0
Register name
1
1
0
1
0
0
0
0
Key scan register
1
1
1
1/0
0
0
0
1
Display data RAM
1
1
0
0
0
0
1
0
X address register
1
1
0
0
0
0
1
1
Y address register
1
1
0
0
0
1
0
0
Port A register
1
1
0
0
0
1
0
1
Port B register
1
1
0
0
1
0
0
0
Control register1
1
1
0
0
1
0
0
1
Control register 2
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