Re: ELF Circuits
- Also, data/address scrambling is also used to make reverse
engineering and copying harder. It won't stop determined efforts, but
it slows things down. Can't just suck the data out of the EPROM
You will also note that vanilla ELF's ignored address bus
multiplexing because the low order address bits were the ones that
remained on the bus during the transfer portion of the memory cycle.
The ELF is a great example of the 1802's ability to minimize logic in
small systems. Some processor architectures that resorted to
multiplexing to save pins combined address and data functionality,
forcing the use of data path wide latches regardless of system size.
Rearranging the address/data pins sometimes makes troubleshooting a
bit of a pain at times, especially when the data/address pins are
arranged on the chip in nice groups. But when the pin arrangement is
somewhat unorganized to start with, it makes little difference.
Also, there's really no problem with using negative logic when
If I recall correctly, ATARI did some funny things with their 400/800
series disk drive subsystems along the lines of using inverted logic
data bus disk controller chips. When they low level formatted a disk,
the empty sectors had $FF's in them instead of the usual $00's. The
IBM standards for Floppy formatting allow this, but most floppy disk
technology users didn't stray too far from IBM's default formats for
what went onto the media. I forget whether the physical media stored
the user's data bytes logic true or false (relative to IBM) on ATARI
800 formatted disks. My memory tickles towards negative logic. Since
it was propriatary, why would ATARI care? It would only make things
harder for the competition.
It really doesn't matter what you use for logic assignments as long
as you are consistent.
Unless you are fixing/troubleshooting/designing, It's usually at the
user interface level that matters.
- I have to laugh.
[Non-text portions of this message have been removed]
That is really funny for those of us "in the know" as to where
they're coming from!
Those two VIP's closed out pretty painfully too: $125 for the lone
VIP, and $225 for the one with monitor & docs.
I was tempted to spring for the lone board for say, $25, but that
would only be for a backup/spare, as I still have my working VIP. The
feedback did indicate that the lone VIP does work just fine though.
At least the winning bidders seemed to be happy with their new toys.
eBay is a strange place.
--- In firstname.lastname@example.org, "J.C.Wren" <jcwren@j...> wrote:
> I have to laugh.
- --- In email@example.com, "sbirdasn" <sbirdasn@y...> wrote:
> Those two VIP's closed out pretty painfully too: $125 for the loneWell... I paid $35 for my VIP a number of years ago (15?), but
> VIP, and $225 for the one with monitor & docs.
> I was tempted to spring for the lone board for say, $25, but that
> would only be for a backup/spare, as I still have my working VIP.
it came with several manuals, a full load of RAM and the blue
plastic cover (unlike the $125 bare VIP), so I'd be surprised
(and pleased!) to get one for even $50 these days.