BU9795AKS2 Datasheet, PDF (11/40 Pages) Rohm – Standard LCD Segment Drivers

BU9795Axxx Series MAX 140 segments (SEG35×COM4)
Datasheet
●Function Description
○Command and data transfer method
○3-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 to D0 are followed after CSB =“L”.
(Internal data is latched at the rising edge of SCL, it converted to 8bits parallel data at the falling edge of 8th CLK.)
CSB
Command
Command/Data
SCL
SD
D/C D6 D5 D4 D3 D2 D1 D0 D/C D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5
D/C = “H” : Command D/C = “L” : Data
Figure 15. 3-SPI Command/Data transfer format
○Command transfer method
After CSB=“H”→”L”, 1st byte is always a command input.
MSB of the command input data will be judged that the next byte data is a command or display data (This bit calls
“command or data judgment bit”).
When set “command or data judge bit”=‘1’, next byte will be (continuously) command.
When set “command or data judge bit”=‘0’, next byte data is display data.
1 Command
1 Command
1 Command
0 Command
Display Data …
Once it becomes display data transfer condition, it will not be back to command input condition even if D/C=1.
So if you want to send command data again, please set CSB=“L”→”H”.
(CSB “L”→”H” will cancel data transfer condition.)
Command transfer is done by 8bits unit, so if CSB=“L”→”H” with less than 8bits data transfer, command will be
cancelled.
It will be able to transfer command with CSB=“L” again.
In Case Of Command Transfer
CSB
Command
SCL
12345678
SD
1
12345678
STATUS
DISCTL Command Transfer
Command Cancelled (Less Than 8bits)
Command
12345678
DISPON Command Transfer
Figure 16. Command transfer format
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