BU9794AKV Datasheet, PDF (6/26 Pages) Rohm – Standard LCD Segment Driver

BU9794AKV MAX 200 Segments (SEG50×COM4)
●Function Description
○Command and data transfer method
○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, followed by D6 – D0 during
CSB =“L”.
(Internal data is latched at the rising edge of SCL, then it is converted to 8bits parallel data at the rising edge of 8th CLK.)
Command
Command / Data
CSB
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 7. 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
Command
SCL
12345678
12345678
12345678
SD
1
STATUS
DISCTL Command Transfer
Command Cancelled (Less Than 8bits)
DISPON Command Transfer
Figure 8. Command transfer format
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10.Apr.2015 Rev.004