MERA-400 minicomputer teardown - Page 1
Forum section: electronics / projects

author: amo
author_rank: Newbie
timestamp: August 01, 2014, 09:07:29 am
content: In EEVblog #612 mailbag I've mentioned in my letter to Dave that I was working on an emulator of late '70 Polish minicomputer MERA-400. It's not only that. I'm basically trying to preserve as much knowledge about this machine as I can (documentation, software, hardware versions and mods, ...). Few weeks ago I had a chance to do a teardown of a unit that is on a display in Warsaw Museum of Technology. My primary goal was to take good high-res photos of all the internal modules (additional goal was to read contents of all EPROMs).Pictures are now online and I thought that oldschool 74xxx porn is always a good watch, so here it is, hope you find it interesting (or at least amusing):http://mera400.pl/GaleriaDescriptions are unfortunately in Polish only, but images are universal. :-) Individual subsections show, in order:CPUFloating point unitMagnetic-core memorySemiconductor memorySystem busCAMAC interfaceStorage interfaceCharacter devices interfaceMEGA memoryMULTIX peripherial processorRTCFew basic facts about the machine:16-bit asynchronous CPU, up to 1 million operations per second48-bit hardware floating point121 instructions1Mword (2MB) total address spacememory segmentation and paging: dedicated memory block for OS + 15 blocks for user programs32 interrupts (maskable, 10 priority levels)

author: alanb
author_rank: Frequent Contributor
timestamp: August 01, 2014, 09:56:02 am
content: Is there a photo of the magnetic core memory?

author: amo
author_rank: Newbie
timestamp: August 01, 2014, 10:07:55 am
content: Quote from: alanb on August 01, 2014, 09:56:02 amNo, unfortunately there isn't, sorry. I didn't have enough time to take the module apart. I was a bit afraid of damaging the core too.

author: alanb
author_rank: Frequent Contributor
timestamp: August 01, 2014, 11:04:21 am
content: It's a pity, I once watched a core store being hand made and have always been amazed at the manual dexterity of the workers threading the tiny ferrite cores.

author: dannyf
author_rank: Super Contributor
timestamp: August 01, 2014, 11:11:27 am
content: The liberal use of jump wires is amazing.Also, are the boards sagging in some of the pictures? or it is a camera distortion?

author: amo
author_rank: Newbie
timestamp: August 01, 2014, 11:35:14 am
content: Quote from: dannyf on August 01, 2014, 11:11:27 amI should probably clarify this a bit: some jump wires are there by design (with starting/ending points marked on a pcb), but there is a lot of modifications done later on by the user. Those are either small mods required to connect, for example, an unsupported device, or bigger ones, like adding new CPU instructions, extending addressing modes or changing interrupt priorities.Quote from: dannyf on August 01, 2014, 11:11:27 amPrototype version of the computer had boards mounted vertically, but it was against USSR regulations which had to be met before the computer went into production. So the design has been changed to comply with the The Rules and now... boards are sagging. :-)

author: amyk
author_rank: Super Contributor
timestamp: August 01, 2014, 12:28:12 pm
content: Quote from: amo on August 01, 2014, 09:07:29 amInteresting. Async designs are quite rare, a schematic would be nice to see - I've only seen these, which are incomplete:http://www.hanssummers.com/ttlcpu.htmlhttp://ixeelectronics.com/openttl/Addressing.html

author: dannyf
author_rank: Super Contributor
timestamp: August 01, 2014, 12:39:24 pm
content: QuoteWhat's wrong with vertical mounting? It would help cooling and provide better structural rigidity.

author: amo
author_rank: Newbie
timestamp: August 01, 2014, 12:46:36 pm
content: Quote from: amyk on August 01, 2014, 12:28:12 pmCPU schematic is here:http://mera400.pl/files/mera400-dtr-t4-cz2-mjc400-schematy.pdfDetailed CPU documentation with finite-state machine diagrams is also available (in Polish):http://mera400.pl/files/mera400-dtr-t4-cz2-mjc400.pdf

author: amo
author_rank: Newbie
timestamp: August 01, 2014, 12:53:58 pm
content: Quote from: dannyf on August 01, 2014, 12:39:24 pmIt was against The Regulations. One does not simply ignore USSR regulations.But seriously, vertical mounting would be so much better, especialy with boards 300x300mm big.

author: dannyf
author_rank: Super Contributor
timestamp: August 01, 2014, 01:09:42 pm
content: Sure. I was thinking that they must have some reasons to favor horizontal mounting. Just curious as to what they are.

author: amo
author_rank: Newbie
timestamp: August 01, 2014, 01:24:29 pm
content: I don't know the real reasons behind and honestly cannot think of any. The only thing I know is that those were the required standards for building computer systems back then, and they wanted to maintain physical compatibility with their systems (which is also questionable).

author: dannyf
author_rank: Super Contributor
timestamp: August 01, 2014, 02:12:13 pm
content: Great. Appreciated.

author: German_EE
author_rank: Super Contributor
timestamp: August 01, 2014, 03:33:36 pm
content: Dzi?kujemy!

author: Vgkid
author_rank: Super Contributor
timestamp: August 01, 2014, 04:38:06 pm
content: Thanks for the teardown, It was interesting to try to find the TI marked 74 logic chips.