exxos's Atari, Amiga & retro forum

So, ACSI2STM. What's that all about, eh?



BW

Interesting, especially the pitfalls of the building step.

sporniket wrote: 21 Dec 2021 05:52 Interesting, especially the pitfalls of the building step.

Sorry that I missed recording the pivot to protoboard, but it was one of those 'ah balls to it, let's try this' things. I thought I'd leave the original plan in at the start to show how often these things go!

BW

Neat!

Treat yourself to a Dremel for Xmas 🎅🏼

dalek wrote: 22 Dec 2021 00:29 Neat!

Treat yourself to a Dremel for Xmas 🎅🏼

An excellent shout. Why didn’t I think of that two weeks ago when the missus asked? :lol:

BW

Watched your video with interest.

However, a quick point, looking at the micro SD adapter boards they would appear to be standard 5v Arduino ones which have on board AMS1117 5v to 3v3 regulators together with LVC125A level converters. The STM32F103 only has limited pins which are 5V TTL compatibile (PA8, PA11, PA12, PB8 - PB15) which are used for the ACSI interface (DB19). The SD interface pins (PA4, PA5, PA6, PA7) ARE NOT TTL compatible!

BluePill STM32F103 pin out
https://github.com/NazimBL/STM32F103/bl ... iagram.pdf

Micro SD https://www.exxosforum.co.uk/forum/viewt ... 29&p=76611

Do you wire it up to 5v and over-run the SDIO i/f (not 5v compatible, 3v3 only) do you under run it off a 3v3 supply or have you made extensive mods to the micro SD board to bypass the 3v3 regulator and the LVC125 3v3 to 5v level convertors?

Please advise

Thanks

Peter

Hi @microman,

This is interesting. I'd not researched the STM32 myself, so wasn't aware there were different voltage tolerances on the pins.

I doubt it's a problem, though, as I suspect the SD card module is merely changing down the 5V inputs for the SD card and not affecting the output. If I had had a 3V3 module when I did that board, I'd have used one as it's silly to have two voltage regulators where one would do.

I really wasn't sure, though, so thought I'd put it to the test.

The result is as below.

Regards,

BW

@Badwolf Good to know it's not going to damage that Blue Pill board!

I do plan on making a few of these at some point...just the usual problem of not enough time & too many things that I want to do! ;) :roll:

It's good to know. I have yet to watch the initial video though :D

Badwolf wrote: 08 Mar 2022 22:54 This is interesting. I'd not researched the STM32 myself, so wasn't aware there were different voltage tolerances on the pins.
I doubt it's a problem, though, as I suspect the SD card module is merely changing down the 5V inputs for the SD card and not affecting the output.

That is true for most SD card modules, they usually perform level shifting with a "simple" 5V tolerant buffer powered at 3.3V. But a few of them use true dual voltage chips and they do might output 5V.

It is normally better to just power the module with 3.3V. Most modules have a jumper than can be soldered to bypass the regulator. Some don't even need this and can operate at either voltage.

Perhaps more important, note that none of the STM32 pins are truly 5V tolerant. Operating with 5V has some limitations. If you check the datasheet, max voltage is specified as VDD+3.6V. That means it is 5V tolerant only as long as it is powered. In this case it means that you should always power up the device before you turn on the computer. Also internal pullups shouldn't be used for 5V inputs.