Piggybacking OS Rom/Eprom?

Larry

unread,

Feb 4, 2006, 9:24:09 AM2/4/06

to

In the January, 1989 issue of Atari Interface Magazine, there was an
article "Install an Alternate Operating System in an XE." I'm sure
that I've also seen this article on the web. This showed how to
"piggyback" a 27128 eprom on top of the OS rom using a switch and
pull-up resistor for selection. I tried this at the time, but never
got it to work reliably. As I recall, sometimes it would boot, and
sometimes it didn't. Has anyone else had success with this approach?
It certainly *should* work, but didn't for me. On a similar note, has
anyone used a 27256 with a switch to accomplish the same thing? Or has
anyone done a "homemade" RamRod--type board with multiple OS? Thanks.
-Larry

JR

unread,

Feb 10, 2006, 3:47:33 AM2/10/06

to

Hey Larry,

I've been meaning to do a mod like this for a long time and just never
quite gotten around to it. Your email got me to thinking about it again
so I tried it out. Using a 27512 with 4 ROMS burned into it in one of
my 800XL's, I was able to switch between them using switches to ground
on pins 1 and 27 (bent up) with 24K pullup resistors to pull the pins
high when a switch is open. I haven't done any extensive testing but I
was able to boot to each of the OS's

Looking at the pinouts a 272001 is pin compatible if you bend out 3 of
the pins and overhang the chip on the left side of the socket. I've
wired up a harness to connect to the last few pins on each side (1-3 and
29-32) to a 16 position rotary switch with pullups mounted on it. I
used an 8 pin socket that I cut in half down the center to plug on to
the bent up pins of the eprom. With this I should be able to get 16 OS's
on one chip with just a single switch. I tested the harness on the
27512 and it works, so now I just have to pick out 16 OS's to burn onto
a 272001....I'll let you know how it works.

Larry

unread,

Feb 10, 2006, 8:11:41 AM2/10/06

to

Hi JR-

That sounds neat. I'll be very interested to see how you come out with
the 272001! 16-in-1 would be very cool, indeed.
-Larry

JR

unread,

Feb 10, 2006, 1:10:49 PM2/10/06

to

Well, I burned 16 OS's to a 272001 and guess what.....It worked like a
charm. I can now have 16 OS's of my choice available at all times.
Also since I don't have to solder any of the wires to the EPROM, I can
have as many OS's as I'd ever need just by swapping the EPROM with another.

So, now I want to know.....what are everyones favorite alternate Atari
OS's and what special features do they have?

Rick Cortese

unread,

Feb 10, 2006, 6:27:54 PM2/10/06

to

All older stuff because I am not familiar with the newer ones with fast
disk drive support.

My favorite when I was programming was Omnimon. Built in ability to
interrupt any program and a combination [monitor, disasm, Primitive DISK
I/O, asm] with a lot of features. Good compatibility too.

For compatibility Omniview was better then Omnimon. There were still
some problems with programs that looked for a modified OS. Built in 80
column support, good compatibility, and IIRC it worked best with the
Newell memory upgrades<built in ramdisk handlers> and with my ATR.

Modified XL. Just added PD hacks like fast FP routines, fast screen
handler, left margin zero, default color darker so it was easier on the
eyes.