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DA852x-UG02-608 Page 28 of 47
User Guide Release 2.0
DA852X E Ink Evaluation Kit
Display Controllers
3.6
Programming Information
This section provides information useful to the software developer in programming an application using the DA852X
device.
The DA852X EPD driver is a very simple device with an SPI interface. Serial data is streamed into the device and
latched by the LATCH signal if the CS signal is high. The last data bit sent will appear at output DD0. Databits in the
bitstream will cause the appropriate outputs to switch to 15volts for a period determined by the BLANK signal.
The E-Paper process requires a differential voltage across each segment, such that +15v will switch the segment to
black, -15v will switch to white. The DA852X driver achieves this using only a 15v supply by switching the Top-
Plane connection as one of its outputs to achieve the differential voltage. This does, however, cause slightly more
complication in the software since the connection designated as the Top Plane must be managed.
Consider two adjacent segments S1 and S0. The connected outputs are D1 and D0 with TOP as the top plane
connection
S0
S1
TOP
D0
D1
Comment
White
White
0v
0v
0v
Initial state
Black
White
0v
+15v
0v
S0 switches on,
S1 remains off
Black
Black
0v
0v
+15v
S1 switches on,
S0 remains on
White
Black
+15v
0v
+15v
S0 switches off,
S1 remains on
White
White
+15v
+15v
0v
S1 switches off,
S0 remains off
As you can see, the outputs D0 and D1 depend upon previous state as well as the desired state. The term state is used
here to denote the desired display condition of a segment, black or white.
For transition between each state, we can express the following relationships.
1. If
any
segment switches from a Black state to a White state, the Top-Plane shall be high, else it is low.
2. For each segment that must switch from Black to White, its Data output shall be zero.
3. If any segment remains constant while the Top-Plane is high, its Data output shall be one.
4. For each segment that must switch from White to Black, while Top-Plane is zero, its Data output shall be one.
In simple terms this means that Data outputs will be the same state as the Top-Plane if they are not to change,
and opposite to the Top-plane if they are to change. It will be understood from this if some segments change
from White to Black, and others from Black to White, then two separate operations are required.
The reason behind this “complication” is to retain charge balancing in the display. It is required that only one packet of
charge switches the display elements in a positive or negative direction. Successive packets in the same direction will
cause overdriving, resulting in a partially stuck segment, which appears as a “ghost”. Another way to view this to say that
DC balance must be maintained at zero.
The following code snippets are provided as an aid to the developer. They are written in ANSI C, so should be
transportable to most development environments with minimal change. They are provided as is.
