Electronics > Microcontrollers

Interfacing to the parallel bus output of an ADC (AD7771) with a microcontroller

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--- Quote from: super7800 on June 07, 2023, 03:05:16 pm ---@ataradov ideally I would get the full 128ks that the ADC is capable of. However, I can slow the DUT down and can live with a lower sample rate. This is very much non-ideal.

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This would require is 3 MB/second, even if you could receive the data.

The best approach with MCUs I see here is to just use multiple SPI interfaces in parallel . They don't need to have any special internal connections, they will just each handle their own line and share the clock. They would place the data into their own linear buffers, so some bit shuffling would be required, but it should not be too hard.

The hardest part here is to actually get the DRDY bit and start reception in time. I'm not even sure it is possible at that rate.

This output format is really not designed to be read by the general purpose MCUs.

Recently we got a WEACT STM32H750 module from digikey and it included an OV2640 camera. Until now i did not look into this, but i guess there is a DVI input peripheral that can be used to pass the ADC data into MCU RAM using DMA. The ADC output signal DRDY would be a fifth data bit so the firmware can later partition the data.
I just looked into the reference manual. They call it DCMI and it includes a HSYNC input that one can use for syncronization.

Regards, Dieter

Yes, MCU with a parallel capture interface may work. But you also need to check the specs, since some of them will not capture arbitrary data without correct HSYNC/VSYNC signals and may include blanking periods.

The most universal parallel capture interface I know of is present in Atmel SAM E70/V7x MCUs. It is just 8-bits, external clock and enable signals that may be permanently enabled. I easily captured 50 MHz stream using it.

@ataradov interesting peripheral. it does have a QSPI peripheral, so I should be able to take data from the ADC and stream it there (to an onboard QSPI chip) until the PC wants it. Or i could use its HSMCI peripheral. It is a bigger IC than what I had before. It will physically fit, but the board will have to be redesigned for 6 layers, which is no big deal. bought a demo board to play with. ATSAMV71XULT.

i will have to think more on using an FPGA. Im most familiar with Xilinx, but all their new ones are BGA, which is a pain to solder, but doable.

Xilinx was bought by AMD? when did this happen lol?



--- Quote from: super7800 on June 09, 2023, 09:17:16 pm ---it does have a QSPI peripheral, so I should be able to take data from the ADC

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Writing to QSPI memory may be slow. If you replace it with QSPI SRAM, it may work, but still may be tight.

In my case I transferred the 50 MHz stream into the USB and let host PC deal with it.

But it also has quite a lot of internal SRAM too.


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