### Connecting a no-NIC 8086 PC to LAN through its parallel port ### | |
Here's the story: I'm the lucky owner of an ancient Toshiba T1100 laptop. This | |
laptop is fitted with an 80C86 CPU, 256 KB of RAM, two floppy drives and no | |
Ethernet port. There is also no way to add an Ethernet adapter. Since the | |
computer doesn't have a hard disk, working on it can get slightly frustrating | |
sometimes (swapping those 720K floppies all the time is fun, but come on). I | |
dreamed about being able to connect this laptop to a big network drive where I | |
could store all my relevant stuff, so the floppy drive would be used only for | |
booting DOS. | |
As a network drive solution, I use EtherDFS. Problem is, I need to connect | |
somehow the Toshiba T1100 to my Ethernet LAN, and without an Ethernet adapter, | |
it's no trivial task. | |
*** PLIP *** | |
PLIP stands for "Parallel Line Internet Protocol". It's a protocol that allows | |
to send and receive packets through the parallel (LPT) port of a computer. | |
While the name suggests it operates at the layer 3 (IP) level, nothing could | |
be less true. PLIP is actually Ethernet-aware, meaning it sends and receives | |
full Ethernet frames. And that's perfect for what I needed to do. | |
*** The PLIP client *** | |
Russ Nelson from Crynwr wrote a PLIP packet driver for DOS. It's a network | |
packet driver that emulates an Ethernet card, and sends/receives frames | |
through the computer's parallel port. Its usage is pretty straight-forward, | |
assuming one knows what IRQ and I/O port the local parallel port runs at: | |
plip -c 0x60 7 0x378 54:52:00:11:22:33 | |
Note: the PLIP packet driver is able to auto-detect the I/O port and IRQ of | |
the LPT port on newer computers (it did so splendidly on my 386SX), but | |
apparently not on 8086-class computers, where it requires those to be passed | |
as arguments. | |
*** The PLIP "server" *** | |
Okay, I have my brave 8086 computer sending Ethernet frames through its | |
parallel port, but what next? I still need to hook somehow its parallel port | |
to my Ethernet LAN. This is where the server part comes in. I thought, | |
"wouldn't it be convenient to have some sort of switch that could have some | |
Ethernet ports and a PLIP access port?". Obviously such hardware contraption | |
doesn't exist (or at least I am not aware of this), but still, there is a | |
solution: use another PC as a switch! There is this YAPCBR project from the | |
university of Bombay that does exactly what I needed: it turns a DOS PC into a | |
switch, operating on packet drivers running on said PC. YAPCBR stands for "Yet | |
Another PC BRidge", presumably in reference to the "PCBRIDGE" tool that does a | |
similar thing (I did not test PCBRIDGE, in my understanding it operates | |
directly on network cards, while I needed a solution that talks to packet | |
drivers). | |
Now, all I had to do was to start my 386SX desktop PC (whose Ethernet card is | |
connected to my LAN already), load the PLIP packet driver additionally to the | |
packet driver related to the 386SX's Ethernet network card, and finally | |
execute YAPCBR. The latter made sure to forward Ethernet frames between my | |
386SX's network card and the PLIP packet driver back and forth. Naturally, for | |
the whole trick to work, both computers had to be connected together with a | |
parallel cable (same kind as used for LapLink-style parallel transfers). | |
+---------------+ +--------------+ | |
| TOSHIBA T1100 | | 386 SX | | |
| | Parallel cable | | | |
| LPT :--------------------: LPT ETH :--------> MY LAN | |
| | | | | |
| PLIP pkt drvr | | <- YAPCBR -> | | |
+---------------+ +--------------+ | |
The 386SX PC | |
acts as a dual | |
port switch. | |
Once all this was set, I could enjoy having Ethernet connectivity on my | |
Toshiba T1100 laptop, meaning the EtherDFS network drive solution was able to | |
load. From now on I could access my multi-gigabytes network drive without | |
having to transfer files on diskettes. | |
Of course having to transform another PC into a PLIP switch isn't very | |
convenient. A more elegant solution would be to use a hardware "PLIP to | |
Ethernet" device, and it would appear that such device actually exists: it's | |
called "plipbox" and it's an open-hardware project from Chris (aka "Lallafa"). | |
Plipbox is designed to provide Ethernet connectivity to Amiga computers, but I | |
suppose it would work just as well with a PC. I did not follow this path | |
though, since I'm already very happy with the YAPCBR solution. If you're | |
curious about Lallafa's plipbox, read more about it on Chris' website at | |
http://lallafa.de/blog/amiga-projects/plipbox/. Another solution could be to | |
buy a Xircom PE3-10BT adapter - it's basically an Ethernet adapter connected | |
to the LPT port, produced by Xircom during the nineties (and increasingly hard | |
to find nowadays). | |
=== Attachments ========================================== | |
plip112.zip | |
ypcbr102.zip |