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tokafondo
PostPosted: Sat Dec 30, 2023 4:34 pm 
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A prototype coaxial cable bus communication system used in the Trend Monitoring System to interconnect intelligent graphics terminals to a host minicomputer is described. The terminals and host are connected to the bus through a microprocessor-based RF modem termed a Bus Interface Unit (BIU). The BIU hardware and the Carrier Sense Multiple Access Listen-While-Talk protocol used on the network are described.


What powers this system? Of course, a 6502.

https://ntrs.nasa.gov/citations/19800009062

Schematics and details in the document


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Volume II -Bus Interface Unit
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BillO
PostPosted: Sun Dec 31, 2023 3:23 pm 
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That's really neat.

It would have been nice if the included the code. Some of those routines might be worth mining.

Apparently NASA use the 6502 quite a bit.

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BigDumbDinosaur
PostPosted: Sun Dec 31, 2023 4:26 pm 
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The communications protocol was interesting and sort of embodied some of the principles of Ethernet, along with some principles of TCP/IP.  I noted a 6522 was used as an I/O device, as was a 6850 ACIA.  The fact that the 6850 was used, and not the 6551, is telling.  Even though the 6850 lacks an on-chip bit rate generator, it is still a better ACIA that the 6551...and that’s not saying much.

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tokafondo
PostPosted: Sun Dec 31, 2023 7:45 pm 
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I read two 6522 actually, to form a 16 bit parallel bus.

There is a document about the software this unit run, but I don't see listings there


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barnacle
PostPosted: Sun Dec 31, 2023 11:34 pm 
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I too was struck by the resemblance to Ethernet, particularly the collision detection/avoidance protocol. Interesting though that they quote a nine-mile packet length, as opposed to the couple of hundred metres of Ethernet.

Neil
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BigDumbDinosaur
PostPosted: Mon Jan 01, 2024 11:49 am 
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barnacle wrote:
I too was struck by the resemblance to Ethernet, particularly the collision detection/avoidance protocol. Interesting though that they quote a nine-mile packet length, as opposed to the couple of hundred metres of Ethernet.

It appears from what I understood of what I read that the instantaneous data rate was actually slow.  That would help to mitigate the transmission line effects inevitable with a long cable run.

An Ethernet segment running through UTP cable is limited to 100 meters, but can extended by using a repeater between segments to restore signal integrity.  It’s possible to get carried away with that and end up with timing violations.

The old “thicknet” (10BASE-5) and “thinnet” (10BASE-2) implementations could go much further...500 meters per segment with thicknet—usually implemented with a low-loss version of RG-8/U coax, or 185 meters with thinnet—usually implemented with RG-58A/U cable.  In the latter 1980s, I did some thinnet installations, but by then 10BASE-T was starting to gain acceptance.  Field-assembling BNC connectors onto stiff coax was not my idea of fun—punching down UTP is relatively painless by comparison.  :evil:

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barnacle
PostPosted: Mon Jan 01, 2024 12:01 pm 
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You'd be amazed how many BNCs I have stuck on the end of cables in my time at the BBC :D

Vampire taps, though...

Neil
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BigDumbDinosaur
PostPosted: Mon Jan 01, 2024 12:12 pm 
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barnacle wrote:
Vampire taps, though...

Fortunately, I didn’t have to deal with those, as I never did a thicknet installation.  That is not to say I didn’t work with RG-8 coax...when I was in the U.S. Navy, I often had to butt heads with thick coax aboard ship.  That stuff was everywhere, it seemed, even inside of the gun turrets.

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