Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
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Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#2I love these types of posts. There is something really interesting about the detective work required to be able to talk to old devices like this.
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#3BYTE magazine, April 1980, page 115.
NEW HIGH-SPEED COMMUNICATIONS BUS: Xerox Corporation recently made a public announcement of a new concept of processor-to-processor communications intended for an office environment. This novel concept is called "Ethernet", and is a result of some of the work being done in their research labs. In this concept, a single coaxial cable is used as a high-speed communications bus between all processors; communication protocol is handled through software or software supplemented by special-purpose hardware. Rumor has it that an Ethernet processor is now being developed by some form of joint arrangement between Xerox and Intel.
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#4Fascinating 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.
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#5What 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.
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#6Fascinating 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.
Kid, you have no idea... ;-)
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#7What 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 want the Alto electrically isolated from the cable so you don't get ground loops and other nasty stuff from the cable.)
The schematic for the transceiver is at: http://bitsavers.org/pdf/xerox/alto/schematics/209926B_Ether...
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#8Fascinating 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!"
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#9Here 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.
Re: Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone
#10Here 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.