I have been glancing at the Winbond NOR-flash SPI devices as a simple means of a future storage/harddrive solution. They are ultra small and can store 16 MB of data. But my system is running at 5V and they are 3.3V devices.

Now, since I am bit-banging SPI using a WDC 65C22S, would it be possible to translate 5V signals to 3.3V (and the opposite for the MISO signal) using resistors or some other means of passive components?

I know resistors introduce some sluggishness in the signal, but I don't really know how much or how to measure/calculate that. I am currently running at 3.6864 MHz and as each write to the 65C22 port will take at least 4 cycles this would be ~1000 ns per change (1000/(3.6864/4)).

EDIT: Perhaps the use of a HCT-device in between MISO on the device and the MISO pin on the 65C22 is enough to handle the input?
EDIT2: The 74HCT125 quad buffer might be a good candidate for MISO, to keep the three-state behavior of the input pin for up to four devices.

/Johan

There are many small level shifters designed to connect (e.g.) Arduino to SD memory cards. The protocol at the simple level is SPI. I use one on my Ruby boards - the 'host' is an ATmega and it all runs at 5v. (SPI clock at 8Mhz)

e.g. https://www.sparkfun.com/products/13743

The schematic is there too..

Now, while I have no direct experience of SPI Flash/EEPROM devices, I do have a lot of experience with SPI access to SD cards - and it's not hard, provided you can arrange your data in 512 byte chunks..

Or just get one of these and pull out the pins used for SPI... Or check the schematic, etc.

-Gordon

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

you can make a bi-directional level-shifter with a single MOSFET.

While not an ideal choice I have made 5V<>3.3V shifter with a 2N7000 and two resistors.

Just google "MOSFET level shifter"

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Bill

Thanks for the tips!

I think I have an SD card breakout board lying around that I bought several years ago which I had completely forgotten about. Might try to revive that.

Also I've been meaning to learn more about transistors to better understand the analog side of digital circuitry so maybe building a level shifter with a MOSFET is a good project to start with.

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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?

Thanks Garth for the detailed explanation. The circuit for the 65C22 outputs looks a bit similar to what I had in mind. I have to admit I don't understand the need for the capacitor and the concept of poles and when I googled it I quickly got lost in math equations. I am clearly lacking some fundamental understanding of analog circuit design in this regard. I also realize that my suggestion of using something like 74HCT125 would require additional combinatorial logic to OR the MISO signal.

_________________
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?

Thanks for a clear explanation. Like you say speed is probably not an issue in this context but might as well adopt a good habit when I am at it. I will consider this going forward. Thanks for the link as well, I guess that post covered mostly what I was asking about (it's a bit tricky to find the right threads in this well of information).

OT: Right now I am stuck with getting my simple 23LCV1024 SPI SRAM to work. I got it working on breadboard several years ago so it's probably a small stupid bug somewhere in the current code.