Hello. I have AD5270 10 bit digital potentiometer and I am writing SPI driver for it.
The wiring is as following:
STM32F407 AD5270
+3.3V ->VDD
GND ->VSS
SPI1_MISO -> (Not currently wired with SDO, SDO is pulled up with 10k)
SPI1_MOSI -> DIN
SPI1_CLK -> SCLK
SPARE_GPIO -> CS
STSM32 SPI configuration:
As you can see form above CPOL = 0 and CPHA = 1 (2 edge) this is required for AD5270.
According to AD5270 documentation:
As you can see from the first image, I am mainly interested in Command number 1 (Write contents of serial register data to RDAC)
C3 C2 C1 C0
0 0 0 1
I am now trying to build a correct frame for writing 10 bit value to set the potentiometer value
I am a little confused regarding MSB/LSB. Could someone clarify How do I build correct frame and which order do I need to send bytes. At the moment, I have written this function:
//WRITE_RDAC = (1<<2),
void AD5270_WRITE_RDAC(uint16_t value){
// first 2 bytes are 0, then 0 0 0 1 D9 D8,
// so the frame look like (when value = 16)
// 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 0
// so the frame look like (when value = 2)
// 0 0 0 0 0 1 0 0 0 0 0 0 0 0 1 0
if(value > 1024){
DEBUG_PRINT("Input value out of bounds \n");
return;
}
uint8_t spi_data[2] = {WRITE_RDAC,value};
AD5270_CS_Enable();
HAL_SPI_Transmit(&hspi1,spi_data, 2, 0xff);
AD5270_CS_Disable();
}Logic analyzer settings:
I tried to execute the following command:
AD5270_WRITE_RDAC(16);And I see on the logic analyzer:
When I try to send:
AD5270_WRITE_RDAC(2);The signal looks like:
I just want to understand whether my frame is incorrect or I should be looking at hardware issues (maybe the chip is faulty or something else). I am monitoring Wiper (W pin on the AD5270) using digital multimeter and it does not change when I send the commands. I expect the resistance to change when I write different values to RDAC. The resistance is always set to 900Ohms and its not changing.
CPOL=0 and CPHA=1 means "shift on rising edge, sample on falling".
On the waveforms you've presented it's the other way round.
Read out and check your SPI registers' setting.
And I'd recommend you to stop relying on Cube.
JW
