Difference between revisions of "Servo 1.0 protocol"
Revision as of 16:21, 11 May 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_servo 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.
The default address of the servo board is 0x86.
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_servo board defines several ports.
|0x20||Set servo 0 position|
|0x21||Set servo 1 position|
|0x22||Set servo 2 position|
|0x23||Set servo 3 position|
|0x24||Set servo 4 position|
|0x25||Set servo 5 position|
|0x26||Set servo 6 position|
The spi_servo board supports two read ports:
|0x01||identification string. (terminated with 0).|
|0x20||read servo 0 position|
|0x21||read servo 1 position|
|0x22||read servo 2 position|
|0x23||read servo 3 position|
|0x24||read servo 4 position|
|0x25||read servo 5 position|
|0x26||read servo 6 position|
read the identification string of the board. ('spi_servo 1.0').
|data sent||data recieved||explanation|
|0x87||xx||select destination with address 0x82 for READ.|