Motor protocol

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Revision as of 16:44, 11 April 2014 by Tom (talk | contribs) (write ports)

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--- 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)
two separate brushed motors section....
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
Stepper motor section....
0x40 set current position. <4 bytes>
0x41 set target position. <4 bytes>
0x42 set relative position. <4 bytes>
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. Requires a write to 0xf1 and 0xf2 first.
0xf1 write 0x55 here to start unlocking the change address register.
0xf0 write 0xaa here to unlock the change address register.
Simple high-side PWM section....
0x50 set PWM value for output B1
0x51 set PWM value for output B2
0x52 set PWM value for output A1
0x53 set PWM value for output A2

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. <4 bytes>
0x41 read target position. <4 bytes>
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 0x12345678

data sent data recieved explanation
0x90 xx select destination with address 0x90 for WRITE
0x41 xx port 0x41: set target position
0x78 xx
0x56 xx
0x34 xx
0x12 xx