With NVRAM you can simply tie the R/W pin to +5V using a 3K3 resistor. Or (if you want to be able to write, but protect the contents against accidental erasure) you could possibly tie the R/W pin to, say, a latch or even a VIA pin (probably best to also have a 10K pull up resistor to deal with tri state before the VIA is programmed).

Something like this:


The only thing I'm not sure of is the need for the pullup resistor on the VIA_PIN line (R1). I've put it in so that you hopefully the NVRAM write pin will never enable writing (logic 0) spuriously (during boot/reset, VIA setup, etc.). As I say, it might not be needed, but its inclusion shouldn't cause any problems and it's best to be safe . The use of HC or AC logic is recommended for the OR gate IC as you don't want to ahve to wait CPU cycles for the state of the VIA_PIN to affect the WE pin of the NVRAM when you decide to change it. Also, having the OR gate introduces a propogation delay which can possibly affect the maximum speed of your design. Fast=Good.

You could also add a hardware switch, operated manually, like the gizmo on floppy discs or SD cards.

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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?

Yes, I think you have to look after write-protect in your own circuit - the chips don't do it for you. You might for example want to write protect only the top part of the chip, containing the vectors and boot code.