Difference between revisions of "Spi lcd 1.3 protocol"
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The addresses on the SPI bus are 7 bits wide. The lower bit specifies if the transaction is to be a read or a write. Write transactions have the lower bit cleared (0), read transactions have the lower bit set (1). |
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Each transaction on the SPI bus starts with the address of the board. The spi_lcd board will ignore any transactions on the SPI bus that do not start with its own address. |
Each transaction on the SPI bus starts with the address of the board. The spi_lcd board will ignore any transactions on the SPI bus that do not start with its own address. |
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After the address a single byte indicates the "port" on the board that the data is written to. The software can thus define 256 ports on each board. |
After the address a single byte indicates the "port" on the board that the data is written to. The software can thus define 256 ports on each board. |
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= write ports = |
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Some ports just set a single value. So writing more than one byte to such a port is redundant. Other ports are logically a stream of bytes. So writing more than one byte is encouraged. |
Some ports just set a single value. So writing more than one byte to such a port is redundant. Other ports are logically a stream of bytes. So writing more than one byte is encouraged. |
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| 0xf0 || change address. |
| 0xf0 || change address. |
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= read ports = |
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The spi_lcd board supports two read ports: |
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{| border=1 |
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! port !! function |
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| 0x01 || identification string. |
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| 0x02 || read eeprom (serial number). |
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Revision as of 11:00, 14 February 2012
The addresses on the SPI bus are 7 bits wide. The lower bit specifies if the transaction is to be a read or a write. Write transactions have the lower bit cleared (0), read transactions have the lower bit set (1).
Each transaction on the SPI bus starts with the address of the board. The spi_lcd board will ignore any transactions on the SPI bus that do not start with its own address.
After the address a single byte indicates the "port" on the board that the data is written to. The software can thus define 256 ports on each board.
write ports
Some ports just set a single value. So writing more than one byte to such a port is redundant. Other ports are logically a stream of bytes. So writing more than one byte is encouraged.
The spi_lcd board defines several ports.
| port | function |
|---|---|
| 0x00 | display data. |
| 0x01 | write data as command to LCD. |
| 0x10 | any data clears the screen. |
| 0x11 | move the cursor to x, y. y is the top 3 bits, x is the bottom 5 bits of the data. |
| 0x12 | set contrast. |
| 0x13 | set backlight. |
| 0xf0 | change address. |
read ports
The spi_lcd board supports two read ports:
| port | function |
|---|---|
| 0x01 | identification string. |
| 0x02 | read eeprom (serial number). |