Xerox Alto's 3 Mb/s Ethernet: Building a Gateway with a BeagleBone

Post by tyingq » Wed, Jan 10, 2018, 2:36 AM UTC

fernly wrote: post #30

thought_alarm wrote: post #28

What makes ethernet "Ethernet"? There's 10BASE-T Ethernet, which is what we all use and has been around since the late 80s. There's 10BASE5 and 10BASE2 Ethernet, which uses a shared coax cable between machines and was around from the early-80s to the mid-90s. And then there's the pre-standard coax Ethernet that the Alto used in the 1970s. Is there a common technological thread between these three things, other than t…

I think the common thread is multiple sender/receivers on a single shared conductor using csma/cd. https://en.wikipedia.org/wiki/Carrier-sense_multiple_access_...

Post by kijiki » Wed, Jan 10, 2018, 2:51 AM UTC

thought_alarm wrote: post #28

What makes ethernet "Ethernet"? There's 10BASE-T Ethernet, which is what we all use and has been around since the late 80s. There's 10BASE5 and 10BASE2 Ethernet, which uses a shared coax cable between machines and was around from the early-80s to the mid-90s. And then there's the pre-standard coax Ethernet that the Alto used in the 1970s. Is there a common technological thread between these three things, other than t…

Post by bsder » Wed, Jan 10, 2018, 3:59 AM UTC

kens wrote: post #23

dfox wrote: post #21

Earlier quoted context omitted.

That is the aforementioned switching power supply. On the other hand what I see as more funky is IC1 and IC02, what exactly is that? Some kind of gated comparator? (Also of note is how IC3A and B has different, but equivalent, logic symbol to IC3C and D)

IC1 is a 75140 dual line receiver, where pin 6 is a reference and pin 2 is a strobe, so pretty much what you thought. Also of interest is IC101, a 75122 triple line receiver, which has a Schmitt trigger, two AND gates and a NOR for each line. Most of the pins are tied to ground (1, 2, 3, 4, 12) so it's used as a buffer, ignoring the rest of the logic. For IC3A-D, I think what's going on with the symbols is a briefly-…

Post by kens » Wed, Jan 10, 2018, 4:08 AM UTC

chrisweekly wrote: post #32

binhex wrote: post #2

I 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.

Agreed! Meta for admins: shouldn't the headline include the year? (I've got comment downvote rights per karma > 500, but can't edit post headlines.)

Post by bsder » Wed, Jan 10, 2018, 5:10 AM UTC

sigstoat wrote: post #26

bsder wrote: post #14

Earlier quoted context omitted.

While I love this (and I am ECSTATIC about the PRU documentation ... thankyouthankyouthankyouthankyouthankyouthankyouthankyou ... I have been using this right now ), I would expect this would have been loads easier with even something really cheap like a MAX10 FPGA. However, he does mention needing a network stack, so maybe not.

> I would expect this would have been loads easier with even something really cheap like a MAX10 FPGA. basically nothing is easier with an FPGA. faster, perhaps.