SC18IS600, SPI command to read internal register always return 0

[idanu357]

Hello,

I'm trying to use SPI to communicate with the SC18IS600 but not getting anything on the miso of the SPI.

As the datasheet example im sending 0x21,0x04,0x00 an expecting to get 0xf0 but nothing comes back on the miso lines of the chip.

I've verified the clock, cs and mosi and i ca see all the signals arriving to the chip and vdd.

im using python and pyftdi library and can communicate with other chips on my board via SPI.

The picture showing the clk and mosi signals to the chip (sorry for the low quality) and i can verify the 0x21 0x04 0x00

any advice ?

 

[ErikaC]

Hello,

Please note that the SC18IS600 is compatible with SPI Mode 3 which means that the SCLK signal should be idle high and data is clocked in and out on the rising clock edge. From your waveforms, SCLK is idle low.

In addition, I don't see a 0X21 in your first byte, it should be 00100001 and I see it stars at 1.

Regards.

[idanu357]

Hello ErikaC,

The last image of the signals was misleading since the signals timing was off.

I managed to get a better one with two live signals (and not using ref signal) to verify that the 0x21 is transmitted correctly.

My problem was he reset pin was set to 0 and not 1

another issue was the command structure, 0x21 0x04 0x00, the 0x00 is redundant and the correct one is 0x21 0x04.

Thanks for your help !