BU2505FV - Can I use SPI with this part?

Question

I am planning to use the BU2505FV DAC in my design and to communicate with it using SPI.

Is the 3 Wire interface described in the datasheet compatible with SPI? The DAC expect 14 bits to configure an output, and my Microcontroller SPI can send only bytes (8 bits per byte). So what will happen if I try to configure an analog output by sending 16 bits (2 bytes) to the DAC?

Also, I plan to connect other devices to the SPI bus, such as the MCP23S17 I/O expander. Are there any compatibility issues with using both parts in the same design?

Thank you all for your help!

Answer 1

Apologies if I'm wrong !

The clearance between SPI and shift register shifting is uncertain. Shifting a shift register with bitbang method isn't a hard thing to do. But, it is doable with SPI.

In the datasheet, there is a nice illustration showing that the device can be cascaded or should I say daisy-chained (like some SPI devices).

Now the implementation, BU2505FV has a 14-bit shift register, so, you have to left-shift the data 2 bit first and then do a ordinary SPI transfer.

A little advice, timing characteristics and pin functionality should be "studied" carefully.

A comfirmation: look at Data Interface section in this product detail.

Answer 2

The only real difference between the chip's serial protocol and SPI is that LD (the Slave Select analogue) must be pulsed high to latch the internal shift register but kept low at all other times. If you add a pulse former to that line you can make it behave like any other SPI device.

When sending 2 bytes the first 2 bits sent will be discarded by the chip (will actually get shifted out of DO with 14 clocks of delay), the rest are as described in the spec.

Answer 3

That part is not SPI compatible. It uses its own serial protocol.