Hi everyone,
- I'm using ADS1198 microcontroller with the AM1808 (SBC8018 board). These two chips communicate to each other via SPI bus. In ADS1198 datasheet I read that the master device (AM1808) need to send "START" command (0x08) to the slave device (ADS1198) via DIN (Data INput or MOSI) line to start conversion, and "RDATAC" (Read Data Continuous Mode) command (0x10). Then, "START" signal must be pulled high. Immediately after that, ADS1198 starts to convert analog signal on input to digital signal on output. When conversion is finished, DRDY (Data Ready) signal is pulled down for one SPI_SCK (serial clock) period and than is pulled up. Data is ready for reading on DOUT (Data OUT or MISO) line.
- I think that this is preety simple communication but I have some problems. I captured the followed signals with oscilloscope: SPI_SCK and I got sequence of bits as well as on the SPI_CS (Chip Select) line. The same situation is on the DOUT (MISO) line - I got sequence of bits but in my terminal (on the PC) I got always the same NEGATIVE values (for example "-1096414160"). It's nothing connected to the analog inputs of ADS1198 so I need to get different values because input voltage varies. In my application I checked whether "START" and "RDATAC" commands are sent via DIN (MOSI) line and everythig is fine. DRDY signal works well - also I got sequence of bits. "START" signal needs to be pulled high all the time but it isn't (it change logical level all the time).
- Where I'm wrong? Why I got the same values although I know that I must get different values?
Thanks in advance,
Vladimir