Motor protocol

--- UNDER CONSTRUCTION!!! --- More info will be added.

Introduction

The protocol for the SPI_motor board will be explained on this page.

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.

Also see the general SPI protocol

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_motor boards defines several ports.

port	function
0x10	Set drive intensity for stepper mode (default is 0x20)
0x20	Spin motor A in direction A with intensity <byte>
0x21	Spin motor A in direction B with intensity <byte>
0x22	Stop motor A
0x30	Spin motor B in direction A with intensity <byte>
0x31	Spin motor B in direction B with intensity <byte>
0x32	Stop motor B
0x40	set current position.
0x41	set target position.
0x42	set relative position.
0x43	set stepdelay. (in tenths of a millisecond, default 200: 20ms between steps).
0x44	Set number of driven coils. Writing 0x00 means driving one coil, other values mean driving two coils
0xf0	change address.

read ports

The spi_motor boards defines the following read ports:

port	function
0x01	identification string. (terminated with 0).
0x02	read eeprom (serial number).
0x40	read current position.
0x41	read target position.
0x43	read stepdelay. (in tenths of a microsecond, default 200: 20ms between steps).

examples

read identification

read the identification string of the board. (spi_motor)

data sent	data recieved	explanation
0x91	xx	select destination with address 0x90 for READ.
0x01	xx	identify
xx	0x73	's'
xx	0x70	'p'
xx	0x69	'i'
xx	...	etc.

move stepper to step 0x1234

data sent	data recieved	explanation
0x88	xx	select destination with address 0x88 for WRITE
0x41	xx	port 0x41: set target position
0x34	xx	low byte
0x12	xx	high byte.