Extra outputs anyone ???

What have you built or do you want to design to go with your replica 1

Extra outputs anyone ???

Postby fsafstrom » Jun Thu 26, 2008 11:03 pm

Here is a simple way to provide some extra outputs in stead of using a 6522 or 6526...

The 1D to 8D goes to the Databus of the 6502.
R/W is the Read Write from the 6502.
PHI2 is the clock from the 6502.
Address Enable is an Active Low enable from an address encoder such as an 74LS138. For example, the $A000-$AFFF, $B000-$BFFF or $C000-$CFFF pins on the Replica expansion port...
And finally the 1Q to 8Q is the actual output.

The three IC's in the picture (74LS02, 74LS08 and 74LS373) should run you about $2 total compare to $8 for the 6522...

Image

Have fun...
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Postby vbriel » Jun Thu 26, 2008 11:52 pm

It's been a long day for me but this is a good low cost output solution.

Now, using a 245 you should be able to do Input and output. Have you thought about using one of those?

Vince
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Postby fsafstrom » Jun Fri 27, 2008 12:07 am

I was thinking of a 244 for the input and just keep input and output on separate addresses. That way I don't have to worry about any data direction registers...

Maybe I could use the 245 to be able to read the current value on the output port...
This solution does not allow you to read the current value that you wrote to the port since it's output only...
On the other hand, it's not really a problem as long as you take that into consideration...
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Postby vbriel » Jun Fri 27, 2008 12:26 am

Keeping a 244 as the input and 373 as output might be better so there is no confusion on direction.

Just a thought, but if you look at your circuit, I think you can combine the gates to 4 NAND's from a 00. It's late and my math might be wrong might want to see, then you can cut it down to just 2 chips. And that was just for the output circuit you did.

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Postby fsafstrom » Jun Fri 27, 2008 12:58 am

Something like the schema below, but I used the 74LS02 (NOR) in stead...

I was thinking of adding another three 373s to get 32 outputs since they are so cheap anyway.
That is why I used the 02 and 08 since they have four gates each...

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