Electronics > Microcontrollers

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

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super7800:
Datasheet: https://www.analog.com/media/en/technical-documentation/data-sheets/AD7771.pdf
Timing found on page 57/58

So i'm trying to interface a SAMD21G18A running an Arduino bootloader with the parallel interface of the AD7771A. There are 6 pins coming from the ADC, four are parallel data, a clock output, and a ready signal. Basically all the makings of a QSPI interface with ADC-as-master.

My first thought was interrupts (basically bit-banging the interface), but that is proving very unreliable. I am wondering how the "correct" way of doing this is? would it be using a QSPI interface? (ideally not as this is a custom board already sitting before me, and the SAMD21 doesn't support QSPI).

I can get the data directly from the SPI interface aswell but that is not ideal. Ideally the data is received as fast as possible (not in samples/s but in processor cycles) so the processor can tend to its main task. Is using a QSPI interface a way to achieve this, the only way, the correct way? alternatives?

ataradov:
What is your MCLK/DCLK?

Without looking into the details of the SPI protocol, I would guess that hardware SPI would be faster than software bit-banging. Especially given that you can do SPI using DMA or interrupts, leaving time for other things to run.

DavidAlfa:
Can it make dma transfers using a Timer?
If so, you could set up a PWM timer at 50% duty, inverted mode (Output low while active) acting as the master clock.
Then setup a second PWM channel in the same timer with no output, set at slighly larger duty cycle (ex. 55%) duty (So it triggers slightly after the first PWM rised, to let the new data signal stabilize), which trigger the DMA.

ataradov:
This is way too complicated, just use DMA with a regular SPI mode.

DavidAlfa:
Ah, it's much easier, the clock comes from the ADC!
Then use the external interrupt controller, generating an event that triggers dma transfer from the GPIO to a circular buffer

It's 32bit per sample (24+8) and SPI Fmax is 30MHz, so with it you can still get ~937KSps, close to the ADC limit.

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