The Dan ][ SD card disk controller

dabone wrote:

CVT wrote:

dabone wrote:

Ok, how about this for 28cXX support?

 

It's pin 27 that the problem,  it's actually A14 on 27256s and 27512s, but the 28c series uses it as the write enable pin.

So for proper address decoding on standard eproms, this pin should be held low, but on the 28c series it needs to be held hig

 

The original design only went as high as 27C128 for the 27-series EPROMS:

Apple2Card.png

There is no need to go higher. The 27C128 chip fits 16K, while the firmware that needs to be written is only 512 bytes: https://github.com/ThorstenBr/Apple2Card/blob/main/eprom/bin/eprom.bin

I currently have around 100 25c512s, and 20 or so w27c512s, and 10 or so 27256s.

So supporting eproms that people may have or use is a good thing. 

It's true that you can just tie that pin high and offset the rom into the bigger chips, but easier if you don't need to.

dabone wrote:

I currently have around 100 25c512s, and 20 or so w27c512s, and 10 or so 27256s.

So supporting eproms that people may have or use is a good thing. 

It's true that you can just tie that pin high and offset the rom into the bigger chips, but easier if you don't need to.

 

You might happen to have lots of those, but larger chips are more expensive and harder to find. So, perhaps going lower instead of higher might be something else to consider, like AT28C16 in DIP24 package.

FYI I've just ordered a batch of boards - they should be available in the UK in the coming weeks. If anyone's interested please dm me. I can also probably prepare full kits (assembled or not).

CVT wrote:

dabone wrote:

I currently have around 100 25c512s, and 20 or so w27c512s, and 10 or so 27256s.

So supporting eproms that people may have or use is a good thing. 

It's true that you can just tie that pin high and offset the rom into the bigger chips, but easier if you don't need to.

 

You might happen to have lo

AT28C64 are super easy to find and reasonably priced.  I've used them in the original DAN ][ design.  Most of the ones I have built I used an AT28C256 ot CAT28C256

I'm doing one more respin of this, and defaulting to pin 27 being tied high for 28cxx compatiblity, but allowing a solder jumper to handle 27 tied low so it can work with 27256s, 27257s, 27512s, and w27c512s.

These will also work with 27 tied high, but then you have to figure out your offset when you burn your image.

That gives the most options and ease of use.

dabone wrote:

I'm doing one more respin of this, and defaulting to pin 27 being tied high for 28cxx compatiblity, but allowing a solder jumper to handle 27 tied low so it can work with 27256s, 27257s, 27512s, and w27c512s.

These will also work with 27 tied high, but then you have to figure out your offset when you burn your image.

That gives the most options and ease of use.

 

&n

Sounds like a plan!