Re: 1551 Repair - 28 pin 6523 Wanted

On 3/8/2014 11:42 AM, Gerrit Heitsch wrote:
> On 03/07/2014 09:55 AM, John McKenna wrote:
>> Excellent, thank you.  That makes a lot more sense. I'll see if I can
>> make it fit a 64/32.
>
> Here's something else I remembered today.
>
> All the 1551 I have seen use a 6525A as the TIA, but I remember seeing 
> an Image of a 1551 PCB that used a 6523A. Looking at the schematics of 
> the drive (*) confirms that the drive does not use the IRQ capability 
> of the 6525, the only IRQ source in a 1551 is a 555 rigged as an 
> oscillator and hooked up to _IRQ of the 6510T. The code seems to be 
> doing everything else by polling (in or out of the IRQ routine).
>
> (*) 
> http://zimmers.net/anonftp/pub/cbm/schematics/drives/new/1551/251860.gif
>
> So, to me it looks like what needs to be implemented to keep our 1551 
> running is an CPLD implementation of the 6523 which is a bit simpler 
> than the 6525.
I believe I have a Verilog implementation of the 6523T, but am working 
on one verilog syntax issue in order to trim the code down to get it to 
fit a 44 pin device, which I can then test in my 1551 (I use a module to 
implement the actual DDR defined register to IO connections, and I want 
to use parms to set the bit length for each port.  I am struggling to 
figure out how to do an "assign" statement in a for loop. Once I figure 
out how to do that, I can trim PORTB and PORTC to 2 bits each via the parm.)

It currently synthesizes into a 9572(XL), but might fit in a 9536(xl) if 
I can trim the 12 bits of unused IO.

For those who want to poke at the code:

Not sure if this link works, but here's the ISE prj: 
https://www.dropbox.com/sh/49jba4d6idwv1af/xaHxce2NIz

And the primary HDL file: 
https://www.dropbox.com/sh/49jba4d6idwv1af/2aY1b2d95W/MOS6523T/cbm6523t.v

Jim

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