Servo 1.0 protocol

Introduction

The protocol for the SERVO boards will be explained on this page.

This page describes both the SPI and the I2C version. See SPI versus I2C protocols for the explanation about how the protocols work in general.

The default address of the servo board is 0x86.

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_servo board defines several ports.

port	function
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
0xf0	change address.

read ports

The spi_servo board supports two read ports:

port	function
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

examples

For SPI in the examples below, "data sent" means the data on the MOSI line, while "data received" means the data on the MISO line. when MISO reads "xx" you should ignore the data. When MOSI reads "xx" it doesn't matter what you send.

For I2C in the examples below, you should first initiate a "write" transaction with the data in the "data sent column". Don't send the "xx" bytes. Then you initiate a "read" transaction, and you will get the data in the "data received" column (and again not the "xx" bytes).

read identification

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.
0x01	xx	identify
xx	0x73	's'
xx	0x70	'p'
xx	0x69	'i'
xx	...	etc.