The Apple ][ floppy controller/6502 doesn't decode the bytes at the
floppy rotation speed. The 6502 copies the encoded bytes (de-serialized
by the controller) into memory, then decodes them after the sector
has been read. The sector interleave guarantees enough time to decode
the data before the next sector is available to be read.
I agree, it is an interesting piece of code...
clint
On Thu, 1 Jun 2000, Sellam Ismail wrote:
> On 1 Jun 2000, Eric Smith wrote:
>
> > Sellam Ismail <foo_at_siconic.com> writes:
> > > But can you dedcode 6&2 encoded bytes in realtime on a 6502? Something
> > > tells me it's not fast enough to do this.
> >
> > If you're clever enough, you can do it. I previously cited several packages
> > that did it.
>
> I'll take your word for it.
>
> > Sellam wrote:
> > > 6 to be exact.
> >
> > 7 to be exact, if you don't count the boot PROM, which isn't really
> > part of the disk controller.
>
> Oh well, I usually get the number wrong no matter how many times I look at
> a ][ controller. At any rate, it's amazing.
>
> I still maintain that the less than 256 byte Disk ][ boot ROM code is one
> of the most amazing pieces of code ever written for a computing device.
>
> Sellam International Man of Intrigue and Danger
> -------------------------------------------------------------------------------
> Looking for a six in a pile of nines...
>
> Coming soon: VCF 4.0!
> VCF East: Planning in Progress
> See http://www.vintage.org for details!
>
>
>
>
Received on Thu Jun 01 2000 - 22:03:39 BST