579 SPI Test
579 : SPI Test
- Author: Harald Pretl
- Description: Simple SPI-based register file (for the testing the flow)
- GitHub repository
- Clock: 20000000 Hz
How it works
A simple serial 16b register (mini SPI) with magic cookie detection is implemented. In addition, a 16bit sigma-delta modulator of 1st or 2nd order is included.
Further, a sine generator (based on a LUT) with programmable frequency can be selected to drive the input of the DAC.
How to test
- Load the shift register in a serial way.
- Check the magic cookie detection.
- Check the digital output (low- and high-byte) of the loaded data word.
- Check the dc output voltage of the delta-sigma modulator by using an external RC lowpass filter.
- Check the sine output of the delta-sigma modulator by using an external RC lowpass filter.
External hardware
Just a way to set digital inputs is needed. A scope for monitoring output signals would be good. A voltmeter can be used to inspect the DAC output voltage. If the sine generator is used for the DAC input, a scope can be used to monitor the sine signal.
IO
| # | Input | Output | Bidirectional |
|---|---|---|---|
| 0 | SPI clk (SCLK) | SPI data out (MISO) | register b0|8 |
| 1 | SPI data in (MOSI) | cookie detected (loaded 0xCAFE) | register b1|9 |
| 2 | SPI load (CS) | XOR of SPI clk and SPI data in | register b2|10 |
| 3 | select output byte (0 = low, 1 = high) | register b3|11 | |
| 4 | sinegen scale factor (LSB) | register b4|12 | |
| 5 | sinegen scale factor (MSB) | register b5|13 | |
| 6 | select ds-modulator input (0 = SPI register, 1 = sine generator) | inverted output of delta-sigma modulator | register b6|14 |
| 7 | order of delta-sigma modulator (0 = 1st, 1 = 2nd) | output of delta-sigma modulator | register b7|15 |