[SOLVED] SPI communication problem

[H2M]

Hi
I want to read data from 16 bits DRV8711 stepper motor driver with an Atmega16 microcontroller by using SPI protocol.
The DRV8711 module have a 16-bit serial write, with a read/write bit, 3 address bits and 12 data bits.
I can correctly write any data to goal register but i cant read from register.
When i want to read data register i have get a 12 bits from DRV8711. how can i get this bits with Atmega16(it is a 8 bits shift register)?
someone help me.
Thanks.

 

[Aussie Susan]

Section 7.5.1 of the data sheet shows how to use two 8-bit exchanges to achieve a 16-bit exchange.
Don't forget that every SPI operation is an exchange. Therefore you need to start by writing a value to the SPI master that will contain the correct bits to request a read, , pick up the value just received, perform a 2nd exchange where you send anything (probably 0x00) and then merge the two received values together to get the 12-bit value.
You will need to select the SPI slave yourself before doing the above and then deselect it afterwards. (At least that is how I read the last paragraph of Page 135 of the Atmega16 data sheet.)
Susan

 

[H2M]

Hi Aussie
I can read correctly DRV8711 registers but i cant correctly merge the two received values. I think the problem are the reserved bits. when i read a register contain reserved bits, what values is the reserved bits? zero? empty?...

 

[FvM]

what values is the reserved bits? zero? empty?...

Why do you care for at all? Just mask them out.

read_val = (read_h & 0xf) <<8 | read_l;