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…

Display Data transfer

Command

●Function description （BU9794KV）

○SPI (3wire Serial Interface)

This device is controlled by 3-wire signal (CSB, SCL, and SD).

First, Interface counter is initialized with CSB=“H", and CSB=”L” makes SD and SCL input enable.

The protocol of 3-SPI transfer is as follows.

Each command starts with Command or Data judgment bit (D/C) as MSB data, and continuously

in order of D6 – D0 are followed after CSB =”L”. (Internal data is latched at the rising edge of SCL,

D/C = “H” : Command

D/C = “L” : Data

Fig. BU9794KV-4 3-SPI Command/Data Transfer format

○ Write display data and transfer method

This device has Display Data RAM (DDRAM) of 50×4=200bit.

The relationship between data input and display data, DDRAM data and address are as follows;

8 bit data will be stored in DDRAM. The address to be written is specified by Address set

command, and the address is automatically incremented in every 4bit data.

Data can be continuously written in DDRAM by transmitting Data continuously.

(When RAM data is written successively after writing RAM data to 31h (SEG49), the address is

returned to 00h (SEG0) by the auto-increment function

DDRAM address

00

01

02

03

04

05

06

07

・・・

2Fh

30h

31h

BIT

0

a

e

i

m

COM0

1

b

f

j

n

COM1

2

c

g

k

o

COM2

3

d

h

l

p

COM3

SEG0

SEG1

SEG2

SEG3

SEG4

SEG5

SEG6

SEG7

SEG47

SEG48

SEG49

As data transfer to DDRAM is done every 4bit data,

it will be cancelled if it changes CSB=”L”→”H” before 4bits data transfer.

○ Reset initialize condition

Initial condition after execute Software Reset is as follows.

・

Display is OFF.

・

DDRAM address is initialized (DDRAM Data is not initialized).

・

Refer to Command Description about initialize value of register.

Command

Command/Data

D5

SCL

CSB

SD

D2

D1

D0

D7

D/C D6D5D4D3D2D1D0

D/C

D1

D0

D7

D6

D6

D5

D4

D3

D6

D5

D4

D3

D2