Using 8 ADC on PGA2350

Support
1

I was thinking of buying the PGA2350 as the description says it has all the GPIO broken out on its RP2350B chip and I’d like to use 8 ADC which reside on GP40 to GP47.

48 multi-function General Purpose IO (8 can be used for ADC)

There is a note about a cuttable trace but I’m not sure what effect cutting it has?

8MB PSRAM (CS wired to GP47 via cuttable trace)

2

And any comment on relevance of RP2350-E9 Erratum: can get "stuck" at 2V state even without pulldown · Issue #401 · raspberrypi/pico-feedback · GitHub to using the ADC (from MicroPython/CircuitPython) would be great

3

There is a note about a cuttable trace but I’m not sure what effect cutting it has?

RP2350 supports an external PSRAM chip, which requires a single CS line to select it. On PGA2350 we include 8MB of that RAM and wired its CS to GP47.

If you need that pin for any other purpose (such as the 8th ADC) and are okay with loosing PSRAM access, then there is a trace on the rear of the board that can be cut to disconnect CS from GP47.

And any comment on relevance of RP2350-E9 Erratum to using the ADC (from MicroPython/CircuitPython) would be great

It is still early days in understanding the behaviour of the RP2350 regarding this. Some discussion is happening here too: RP2350: Internal pull down issue

Hope that helps

4

Thanks, I’ll hold off a bit on the purchase to wait for the dust to settle on the ADC/input issues.

Would be interesting to know why GP47 was chosen for the chip select. Given it has special functionality (the ADC) it doesn’t seem like the optimal choice.

5

Would be interesting to know why GP47 was chosen for the chip select.

Only 4 pins can be used for PSRAM CS, those being GP0, GP8, GP19, and GP47.

GP0 is one of the default UART pins, so that’s out, and GP8 and GP19 are within the middle of the pin range, so would limit possible PIO/HSTX use cases that use a lot of pins in parallel. GP47 seemed the least objectionable.

Since there is the cut trace though, it would not be hard to cut it and solder the CS to one of those other mentioned pins, then spin up a new Micropython build with the new pin.

6

Thanks, I cut the trace and got it going but haven’t yet explored the 8 ADC, that’s next part of project. Did a bit of interim stuff with synthio: CircuitPython synthio on PGA2350 (or Maker Pi Pico)