Hey everyone! This topic has come up a lot, I searched the internet and forum and did not find what I was looking for.

Let's start here, the SPI-10 interface:
viewtopic.php?t=4264

I want to take 5V signals (CS/SCK/MOSI) down to 3V3. I'll worry about the MISO line later.

I found this:
https://hackaday.com/2016/12/05/taking- ... -shifters/

And honestly I think the "two resistors" idea is fine. And perhaps it is. But I'm wondering what you think.

What I am REALLY looking for is a DIP-8 IC that turns 3x 5V lines into 3x 3V3 lines. That would be perfect. I have seen the 74HC4050 and that seems to be exactly what I want, but in DIP-8 package (i.e. less lines, smaller package, still DIP). Any ideas on how to find that?

Also, maybe this is just stupid of me, but why don't I just use a 74LS04? Send in 5V, output is 3.3V, double not gates, out comes what I want. Am I missing something there?

What do you use for level shifting SPI?

Any insight is welcome, just looking for ideas. Thanks everyone!

Chad

I haven't needed to do this level shifting myself yet, but the technique I've always had in mind for unidirectional shifting was to use a 74HC245 or similar transceiver to buffer up to eight (or four if you get the 74HC243) 5V=>3.3V signals, with its VCC at 3.3V so it doesn't output more than that to the 3.3V end. You still need current-limiting resistors from the 5V end, but it has internal diodes that are specified to be fine for this purpose, so you only need the one resistor per input.

For the other way I might use 74HCT245 which has TTL-level inputs so should be fine being triggered by 3.3V even with VCC at 5V, being careful to ensue the direction pin is hard-wired the right way around. To me this is a very simple way to achieve it without using specialist parts.

Edit: I guess there's also the LVC range, e.g. 74LVC245, which are 5V-tolerant and don't require current-limiting resistors.

I didn't realize the 74LVC245 was available in DIP, I thought that the family had only SMD parts. Nice find!

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The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

First, thanks George. I looked more into that 74LVC' ICs and I think I like them! I found Mouser has a thousand 74LVC244's right now in DIP form. So, power them with 3.3V right?



That simulation REALLY hit home. Wow. And just like you said, a triangle wave if you oscillate fast enough! Makes me think of making a triangle wave circuit now

Overall, good info there, thank you Garth.

So I've been thinking about going in reverse with MISO for a while, and I have 1/2 of an LM393 left over from other stuff. Attached is what I *think* would work for MISO (mine is on PA6 in particular here). The 8.2K and 4.3K tied to 3V3 making a 'low' level of 1.1 V. So then comparing to 1.1V we get either high or low. Because the comparator could oscillate if left untied, I put a big 100K pull-up resistor on it, so leaving the comparator as high-Z. And then finally the 10K pull-up resistor brings it to 5V. Now, this MISO is tied to other 5V components, but... I think this should work? Thoughts? It's almost my first time trying this analog stuff out on my own. I'm open to all criticism!

Thank you again everyone!

Chad

_________________
http://WilsonMinesCo.com/ lots of 6502 resources
The "second front page" is http://wilsonminesco.com/links.html .
What's an additional VIA among friends, anyhow?

If your speed requirements are not too ambitious you can just use a simple 2N7000 MOSFET and one or two resistors.

This is a high to low translator:


This is a low to high translator:


And here is a bi-directional:




The following are waveforms @ 55Khz using 3.6K pull-ups. You can see they would work quite well up to about 500KHz. I have been able to do 1MHz using 470 ohm pull-ups, but I don't have any waveforms to show you. I did these measurements with 3V for low side. They will actually work a bit better with 3.3V

High level source:

And corresponding low level output:




Low level source:

And corresponding high level output:

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Bill

Yes the offerings are limited in regard to TH parts. Digikey lists the 74C906 as obsolete, no stock, although it may be available through other channels. But there are lots of surface-mount options, such as 74LV07 and 74LVC07.

BTW this is a good example of why I'm a fan of Digikey's product search. 74C906 is not a part you'd discover by searching for 74*07. That's why I prefer to search based on functionality (not a preconceived part#). Go to...

Product Index ->
Integrated Circuits (ICs) ->
Logic - Buffers, Drivers, Receivers, Transceivers

... then filter the results according to speed, price and whatever else concerns you.

-- Jeff

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In 1988 my 65C02 got six new registers and 44 new full-speed instructions!
https://laughtonelectronics.com/Arcana/ ... mmary.html

If you want to go this route, you can also buy some handy breakout boards that take up very little space and are breadboard-friendly. They come with 10k resistor, so they won't work at super-high speeds, but I've successfully used them for SPI in the past.

It is good to see all the different ways y'all tackle this problem. I like a lot of these ideas and will be considering them all going forward. In the least, I hope that this topic can be easily searched on the forum as well for later use.

Thank you all!

Chad

There are a few modules going around online that are basically four of the bi-directional transistor circuits that BillO mentioned, all on one board, approximately the size of a wide DIP12. I know you can get them from places like Adafruit and Sparkfun, but I found a pack of 10 for a fraction of the price on AliExpress. They seem to work so far, though I haven't carried out much in the way of testing yet.

If it's just for an SD card then there are some excellent pre-made modules from Adafruit and Sparkfun - I use them on my Ruby boards - far easier than fiddling with shifters and using your own sockets, etc.

e.g.

Sparkfun:

https://shop.pimoroni.com/products/spar ... 7290596423

Adafruit:

https://shop.pimoroni.com/products/adaf ... =370780217

On my Ruby 816 board:

https://unicorn.drogon.net/IMG_20200625_212146_DRO.jpg

-Gordon

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--
Gordon Henderson.
See my Ruby 6502 and 65816 SBC projects here: https://projects.drogon.net/ruby/