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OLED display details
As noted here, there are three specific SPI commands that need to be sent which reflect the orientation of the display; the table below reflects what these values are relative to the orientation of the ZedBoard.
| Command | Normal | Inverted |
|---|---|---|
| Segment Re-map | 0xA0 |
0xA1 |
| COM Output Scan Direction | 0xC0 |
0xC8 |
| COM Pins Hardware Configuration | 0x00 |
0x20 |
The OLED display has a width of 128 pixels and a height of 32 pixels (128x32); each character displayed has a width of 8 pixels and a height of 8 pixels (8x8) which results in 4 usable rows each of which can hold 16 characters.
A 2D array of size 4x16 holds 64 characters which are represented by 8-bit (1-byte) ASCII hexadecimal values. The ASCII hexadecimal representation of Hello world! is:
0x48 0x65 0x6c 0x6c 0x6f 0x20 0x77 0x6f 0x72 0x6c 0x64 0x21 0x20 0x20 0x20 0x20
H e l l o w o r l d !
Since each character has a width of 8 pixels and a height of 8 pixels, a single 8-bit (1-byte) value will represent a single column; therefore, in order to display a single character, 8 (one for each column) 8-bit values must be sent via SPI to the display. When displaying any arbitrary ASCII hexadecimal character, the hexadecimal representation is used as the starting memory address to reference the 8-bit values required to display the character; for example, when displaying H (0x48) the following memory addresses hold the 8-bit values sent to the display, these addresses contain hexadecimal values which represent 8-bit (1-byte) binary values:
| Column | Address | Hexadecimal | Binary |
|---|---|---|---|
| 0 | 0x48 & 000 |
0x41 |
0100 0001 |
| 1 | 0x48 & 001 |
0x7f |
0111 1111 |
| 2 | 0x48 & 010 |
0x08 |
0000 1000 |
| 3 | 0x48 & 011 |
0x08 |
0000 1000 |
| 4 | 0x48 & 100 |
0x08 |
0000 1000 |
| 5 | 0x48 & 101 |
0x7f |
0111 1111 |
| 6 | 0x48 & 110 |
0x41 |
0100 0001 |
| 7 | 0x48 & 111 |
0x00 |
0000 0000 |
When a bit is set to 1, that indicates that the corresponding pixel should be turned on; the following grid shows how the bits correspond to individual pixels used to depict the ASCII character H on the display.
Column 0 (0x41) |
Column 1 (0x7f) |
Column 2 (0x08) |
Column 3 (0x08) |
Column 4 (0x08) |
Column 5 (0x7f) |
Column 6 (0x41) |
Column 7 (0x00) |
|---|---|---|---|---|---|---|---|
1 |
1 |
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1 |
1 |
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1 |
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1 |
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1 |
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1 |
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1 |
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1 |
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1 |
1 |
1 |
1 |
1 |
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1 |
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1 |
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1 |
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1 |
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1 |
1 |
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1 |
1 |
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