DIO protocol

Introduction

The protocol for the SPI_dio, SPI_3FETs and SPI_7FETs will be explained on this page. Most functions apply to all three boards, but some don't.

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_dio, spi_3fets and spi_7fets boards define several ports.

port	function
0x10	set all outputs (bit 0 is output 0, etc).
0x20 .. 0x27	set one output (0x20 for output 0, 0x21 for output 1 etc)
0x30	define pins as inputs or outputs. 0 means input, 1 means output.
0x40	set current position. (only spi_dio and spi_7fets)
0x41	set target position. (only spi_dio and spi_7fets)
0x42	set relative position. (only spi_dio and spi_7fets)
0x43	set stepdelay. (in tenths of a microsecond, default 200: 20ms between steps). (only spi_dio and spi_7fets)
0xf0	change address.

All the above ports are read/write. I.e. if you read from that port, you will get the current value.

read ports

The spi_dio, spi_3fets and spi_7fets boards support the following read ports:

port	function
0x01	identification string. (terminated with 0).
0x02	read eeprom (serial number).
0x10	read all inputs
0x20 .. 0x27	read one input (0x20 for input 0, 0x21 for input 1 etc)
0x40	read current position. (only spi_dio and spi_7fets)
0x41	read target position. (only spi_dio and spi_7fets)
0x43	read stepdelay. (in tenths of a microsecond, default 200: 20ms between steps). (only spi_dio and spi_7fets)

examples

read identification

read the identification string of the board. (spi_dio)

data sent	data recieved	explanation
0x85	xx	select destination with address 0x82 for READ.
0x01	xx	identify
xx	0x73	's'
xx	0x70	'p'
xx	0x69	'i'
xx	...	etc.

turn on all outputs

data sent	data recieved	explanation
0x88	xx	select destination with address 0x88 for WRITE
0x10	xx	set outputs as in bitpattern (next byte)
0xff	xx	All outputs active.

turn on output 4

data sent	data recieved	explanation
0x88	xx	select destination with address 0x88 for WRITE
0x24	xx	port 0x24: output 4...
0xff	xx	... active.

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.