Electronics > Microcontrollers

DAC and ADC on one parallel bus on a Pico

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DocRaptor:
Hello,
I want to hook an ADC, more specific an ADC1173, and a DAC, which will consist of a 74AHC373 and a discrete R2R DAC, on a single databus and use a single Nand gatter to switch between them. I want to do this to save pins on a Raspberry Pico for other things. My question is if the 74ahc family quick enough this? I want to use the ADC at 10 to 15 msps and when the PIO is pulling data from the ADC and pushing it in to the TX FIFO, I plan it to switch to the DAC after each sample and pull from the RX FIFO 8 bits and push them to the 74AHC373.

xvr:

--- Quote ---My question is if the 74ahc family quick enough this?
--- End quote ---
Yes. It can operate up to 50-100MHz. But you ask wrong question - will RPi Pico fast enough to sync-on-adc/read/set-oe-to-1/change-direction-of-pins/write-data/write-strobe/change-dir-back/set-oe-0 (all of this) with 15MSps rate? Programmable GPIO in RPi Pico can do 1/2 bit activity, but it can't manage 8 bit port read/write.

TomKatt:

--- Quote from: xvr on June 24, 2024, 12:15:47 pm ---
--- Quote ---My question is if the 74ahc family quick enough this?
--- End quote ---
Yes. It can operate up to 50-100MHz. But you ask wrong question - will RPi Pico fast enough to sync-on-adc/read/set-oe-to-1/change-direction-of-pins/write-data/write-strobe/change-dir-back/set-oe-0 (all of this) with 15MSps rate? Programmable GPIO in RPi Pico can do 1/2 bit activity, but it can't manage 8 bit port read/write.

--- End quote ---
That's what I'm thinking also...   I view the Pi as more of a cpu with GPIO than a dedicated microcontroller - it's great for running an OS but not the fastest when it comes to direct IO control.  It's quite possible that an SPI or I2C ADC / DAC setup would be more efficient on a Pi.

xvr:

--- Quote --- I view the Pi as more of a cpu with GPIO than a dedicated microcontroller
--- End quote ---
PI Pico is a microcontroller, not a big CPU. It will not run OS (except FreeRTOS may be), but IO speed problem still exists.
It probably can run DAC/ADC service, but it will take almost 100% of CPU, I guess.
May be second core will help (it's 2 core MCU), who knows  :-//

DocRaptor:

--- Quote from: xvr on June 24, 2024, 05:14:42 pm ---
--- Quote --- I view the Pi as more of a cpu with GPIO than a dedicated microcontroller
--- End quote ---
PI Pico is a microcontroller, not a big CPU. It will not run OS (except FreeRTOS may be), but IO speed problem still exists.
It probably can run DAC/ADC service, but it will take almost 100% of CPU, I guess.
May be second core will help (it's 2 core MCU), who knows  :-//

--- End quote ---

I won't use the two MCUs Cores. I will use one of the PIOs, which are made for this. 10MSPS to 15MSPS (But I lean more to just go with 10MSPS) is in low side of what people did. One person pushed it (with a different ADC) to 100MSPS using PIOs, DMA, and wrote it in python.
In case I can not let the DAC and the ADC1173 share one bus I would go with the LTC2315-12 as the ADC (with the DAC I would need to look). It is only 5MSPS (I wish more but if it is not posible I have to live with it), but it is a 12 bit ADC and it uses a SPI-interface. The reason for these to is that I set me a limit of 10€ max for the ADC.

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