DIO protocol
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 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) |
| 0x40 | set/read current position. |
| 0x41 | set/read target position. |
| 0x42 | set/read relative position. |
| 0x43 | set/read stepdelay. (in tenths of a microsecond, default 200: 20ms between steps). |
| 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_lcd board supports two read ports:
| port | function |
|---|---|
| 0x01 | identification string. (terminated with 0). |
| 0x02 | read eeprom (serial number). |
examples
read identification
read the identification string of the board.
| data sent | data recieved | explanation |
|---|---|---|
| 0x83 | 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
move to line 1, character 5:
| data sent | data recieved | explanation |
|---|---|---|
| 0x88 | xx | select destination with address 0x82 for WRITE |
| 0x10 | xx | port 0x10 all outputs in bitpattern. |
| 0xff | xx | All outputs active. |
turn on output 4
Turn on output 4.
| data sent | data recieved | explanation |
|---|---|---|
| 0x88 | xx | select destination with address 0x82 for WRITE |
| 0x24 | xx | port 0x24: output 4... |
| 0xff | xx | ... active. |
move stepper to step 0x1234
move to line 1, character 5:
| data sent | data recieved | explanation |
|---|---|---|
| 0x88 | xx | select destination with address 0x82 for WRITE |
| 0x41 | xx | port 0x41: set target position |
| 0x34 | xx | low byte |
| 0x12 | xx | high byte. |