x86/DOS system backup via rs232?

[Fred Cisin]

On Sat, 14 Nov 2015, william degnan wrote:
> I have a copy of the laplink software should anyone need it.  If the cable
> for parallel is just a null modem I suggest a person in this hobby
> definitely add laplink to the bag of tricks available.  You just fire it up
> on both ends ll.exe ...  and you'll see a directory tree of target  machine
> on the right, the source machine on the left.  Pick files and copy.  Copies
> recursively etc.

All Centronics ports have 8 bits going one way, and 4 "handshake" bits 
going the other way.

IFF you can run doftware of your choice on both ends of the cable, Laplink 
and its imitators (such as Interlink) can work just fine.
NOTE: I tend to think of Traveling Software's "Laplink" as being "the 
first", but, as always, there's bound to be a few examples of prior art.
(Such as when did Chuck make his?)
The Laplink cable is a "null printer" cable using those 4 bits.
https://en.wikipedia.org/wiki/LapLink_cable
it is a defacto standard; Chuck's cable was compatible.

Some Centronics compatible printer ports have bidirectionality of the 8 
data lines, and therefore shouldn't need to do nibble transfers using 
"handshake" signals.  But, you can't always count on the other end having 
that.

And, CAN you run software of your choice on both ends?
Ever try to get document files out of a really alien word processor?
But, sometimes that alien machine, with no practical way to run your 
software might output perfectly normal "centronics" printer output!

About 25 years ago, I put together a somewhat special cable, and "printer 
emulator" software to run on a PC.  With the software running on the PC, 
and special cable, I could simply tell the alien machine that it was 
connected to a simple ASCII printer, and tell it to print the document(s). 
The PC would pretend to be a [very fast] printer, and store whatever was 
coming through that "printer" cable that the alien machine was feeding.

Ran into a couple of problems.  Some machines sent a strobe that was 
so substantially shorter than the standard, that I couldn't respond 
fast enough with polling nor interruptws, so I added a one-shot to the 
cable to extend it to the spec duration for those machines.

I put the cable switch-overs and the oneshot into a hooded 
blue-ribbonF/DB25M adapter, so that it could hang off the back of the PC, 
and the alien printer cable could connect to the blue-ribbon connector.

Then I found out just how futile it was to develop a product that few 
understood.  The purpose was not for doubling Laplink's speed, it was for 
capturing printer output from alien machines.  Many people INSISTED that 
Laplink could install itself through the parallel port onto ANYTHING. 
ABSOLUTELY ANYTHING.  Some of the same people insisted that one of the 
competitors to Chuck's and my programs could read ABSOLTELY ANY disk 
format (disunirregardless of hardware incomapabilities).  A few others 
wanted to know how to connect it to machines that did not connect to 
Centronics compatible printers, including ones with built-in printers.
After 5 days at Comdex, I realized that the people who could appreciate it 
was such an infinitesimal subset of the people who needed it that it was 
unmarketable.

A slightly slower similar solution was already possible by connecting the 
parallel output of the alien machine to a parallel-to-serial printer 
adapter, and then using off-the-shelf serial software on the PC to capture 
that.

So, I never brought the product up to marketable form, and 
XenoComm-Parallel joined XenoFont.  Not with a bang, but a whimper.


--
Grumpy Ol' Fred     		cisin at xenosoft.com