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Forum Index : Microcontroller and PC projects : PicoMite RP2350B DIL Development board, 16Mb flash + 8 MB PSRAM

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matherp
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Joined: 11/12/2012
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Posted: 04:51pm 27 Jun 2025

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Slightly modified layout based on constructive (blunt) criticism on the Raspberry Pi forum. Probably makes no functional difference but definitely better.

Gerber_PCB1_2025-06-27.zip

BOM_Board1_PCB1_2025-06-27.zip

PhenixRising
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Joined: 07/11/2023
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Posted: 04:58pm 27 Jun 2025

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Is there a prize for guessing? I ain't gonna win

matherp
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Posted: 05:10pm 27 Jun 2025

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Quote The power layout (looking at the image on the site you linked to) seems poor. Obviously it's constrained by being 2-layer and narrow, but the track running under the chip to connect the boot button is inexcusable - cutting off the ground to the decouplers on the left hand side, when there's plenty of space to take it up the edge close to the row of DIL pins. Also R87 (boot switch resistor) is in the wrong place - should be close up to the flash chips such that the long wire leading to the boot switch doesn't load/put reflections on the timing-critical flash nCS. C101/102/109 all sharing a (distant) GND via isn't ideal either.

PhenixRising
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Posted: 05:18pm 27 Jun 2025

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I cut the ground off also but as Mick pointed-out, the circuit continuity-test in SL6 made it obvious. Such a great layout tool.

scruss
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Joined: 20/09/2021
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Posted: 06:26pm 28 Jun 2025

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matherp said Slightly modified layout based on constructive (blunt) criticism on the Raspberry Pi forum. Probably makes no functional difference but definitely better.

Sorry about that. I thought twice about using the term "overclocking" when I posted the link, as certain users over on the RaspberryPi site have a fundamentalist approach to that word.

matherp
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Posted: 08:05am 29 Jun 2025

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No problem, the layout comments were valid but for overclocking they haven't explored the issues when you need to write to flash and whatever they believe my board overclocks better in an MMBasic environment than the Pimoroni.

Bleep
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Posted: 08:54am 29 Jun 2025

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The guy making the comments isn't a Pi engineer, probably just someone who likes telling everyone how bad everyone else's designs are! If you're happy to make the changes and they seem reasonable, then just ignore the bluntness :-) some people are like that.

javavi

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Posted: 09:46am 29 Jun 2025

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@matherp
Overall I like your design of the RP2350B DIL 64 module

I don't quite understand why the choice fell on the GP0 pin for the CS PSRAM signal? For the RP2350B chip, it would be more logical to use the last port GP47, or to provide the ability to select using soldered jumpers.

matherp
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Posted: 09:51am 29 Jun 2025

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Quote GP47 is much harder to route and the lines need to be kept as short as possible. A selectable link would increase the routing length and if you did that you couldn't then route both to I/O pins as you would have a long routing on the end of PSRAM SS.

javavi

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Posted: 09:57am 29 Jun 2025

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@matherp
Still, I think that it would be possible to bring out the GP0 port to pin 3, for those who are not going to use the PSRAM on the module.

matherp
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Posted: 10:00am 29 Jun 2025

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My choice. If you want to do that then here is the current easyeda design file

Pico2350DILV1.2.zip

Mixtel90

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Joined: 05/10/2019
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Posted: 11:48am 29 Jun 2025

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I completely support GP0 for PSRAM select. It's actually the only logical choice in MMBasic. Only four alternative pins are possible: GP0, GP8, GP19 and GP47.

GP8 is the default MMBasic pin for COM2, used for PS2 keyboards and the console port on HDMI systems. Yes you can change it, but it can be awkward in some cases.
GP19 is one of the HSTX pins so cannot be used on HDMI systems.
GP47 is one of the eight ADC input pins. If you use that then *someone* will want all eight...
GP0 has no default function in MMBasic.

Why complain about GP0 not being available when there is a complete 16-bit port no longer interrupted by ADC pins from GP20 upwards? :)

Mick

Zilog Inside! nascom.info for Nascom & Gemini
Preliminary MMBasic docs & my PCB designs

PhenixRising
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Posted: 05:21pm 29 Jun 2025

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My in-depth review: It's perfect

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