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DAC39J84: SPI 3 wire Communication

Part Number: DAC39J84


I am using DAC39J84 with 3 wire interface (SDIO) for communication. I left SDO open on the board, on the assumption that I should be able to read and write the through SDIO according to the datasheet

"The serial port of the DAC39J84 is a flexible serial interface which communicates with industry standard
microprocessors and microcontrollers. The interface provides read/write access to all registers used to define the
operating modes of DAC39J84. It is compatible with most synchronous transfer formats and can be configured
as a 3 or 4 pin interface by sif4_ena in register config2. In both configurations, SCLK is the serial interface input
clock and SDENB is serial interface enable. For 3 pin configuration, SDIO is a bidirectional pin for both data in
and data out. For 4 pin configuration, SDIO is bidirectional and SDO is data out only. Data is input into the device
with the rising edge of SCLK. Data is output from the device on the falling edge of SCLK"

Now, the question is I want to read back the registers I have written to make sure it is correctly wirtten. To do so, I started with trying to read vendor ID of DAC39J84. I don't see any readback value on the SDIO line. I want to confirm, whether I can read-back in 3-wire mode or I must use 4-wire mode for readback ?



  • Venu,

    SDIO works the same whether using 3 wire mode or 4 wire mode. I would suggest first verifying your writes work by placing the part in power down mode and verifying a drop in current. After you have passed this test, do a write then read of a register you can write to. Vendor ID is not a good register to test with as the ID does not always match the data sheet value and this is a read only register.