11–20 of 44 posts
Here at NASA Goddard, old wiring is often never removed. In the cable trays in the hall outside my office is some ancient coaxial Ethernet cable. At one point, there is a tap and one of the standard cables that went from the tap to a workstation. I keep thinking I should grab the tap and squirrel it away as a historical artifact.
Fascinating to learn that the Ethernet design of the Alto influenced the design of TCP. This might be common knowledge to those who lived through that era but as a millennial I wasn’t aware of this.
The story is that the PARC engineers went to the TCP design meetings, but Xerox lawyers wouldn't let them say anything about Pup. So the PARC engineers would just ask questions until the TCP designers realized the flaws in their proposals: "Have you considered what would happen if..." And the TCP designers would go, "Hey! You've done this before, haven't you!"
If you can take the time it's a great way provide technical feedback in a way that isn't hostile and keeps an open dialog.
How did we make a similar adaptor in the 80'ies with a microprocessor running 2 MHz? Fortunately the PLA was invented. A few bits of memory and a little programmable logic. Enough to synchronize to the, in this case 2.35 MHz, Manchester coded bitstream and assemble the data bits into bytes. The processor was still not fast enough to handle the control bytes of the data stream in real time. It could actually handle th…
However, he does mention needing a network stack, so maybe not.
Here at NASA Goddard, old wiring is often never removed. In the cable trays in the hall outside my office is some ancient coaxial Ethernet cable. At one point, there is a tap and one of the standard cables that went from the tap to a workstation. I keep thinking I should grab the tap and squirrel it away as a historical artifact.
Vampire tap. You had to place them at marked locations on the coax because of signal reflections.
Here at NASA Goddard, old wiring is often never removed. In the cable trays in the hall outside my office is some ancient coaxial Ethernet cable. At one point, there is a tap and one of the standard cables that went from the tap to a workstation. I keep thinking I should grab the tap and squirrel it away as a historical artifact.
What is inside the Alto's ethernet transceiver? From the remark that interface between Alto and transceiver is TTL I gather that it is not same as 10M one (which transformer-coupled RS-422-ish differential interface) and also the collision signal detected by transceiver should probably be different.
The transceiver basically has three parts. There's the logic side connected to the Alto, which XORs the sent data and received data to see if there's a collision. The cable-side circuitry has some analog stuff to put signals in and out of the coax. These two sides are connected via transformers for isolation. Finally there's a simple switching power supply to provide isolated 5.7V to the cable-side circuitry. (You wa…
Earlier quoted context omitted.
Vampire tap. You had to place them at marked locations on the coax because of signal reflections.
And because at that point the shield wires were spaced further apart so as not to short out the connection.
Earlier quoted context omitted.
The transceiver basically has three parts. There's the logic side connected to the Alto, which XORs the sent data and received data to see if there's a collision. The cable-side circuitry has some analog stuff to put signals in and out of the coax. These two sides are connected via transformers for isolation. Finally there's a simple switching power supply to provide isolated 5.7V to the cable-side circuitry. (You wa…
Interesting, I wonder what the funky magnetically-coupled circuit with Q1 and Q2 is for.
Earlier quoted context omitted.
Interesting, I wonder what the funky magnetically-coupled circuit with Q1 and Q2 is for.
That's the switching power supply for the circuitry on the coax side of isolation. The coils are coupled to E, F, G which feed the 5.7V power supply on the previous page.