7xbus 3V3 2mm system; RCBus adapter; and portable VMEX/ASLIX effort;

[7alken]

hi all, as I searched for 44pin CF-card right-angle socket connector, I found only few and quite expensive, but this 2mm connectors browsing lead me to searching for something smaller for 3V3 bus - initially I tried 50pin, but not found entire sets available and cheap, then tried 40pin, then 32pin (all the same issue) and then I found 30pin (2x15), which are available in quite decent quantities at digikey/mouser and are "cheaper" - the more in larger volume orders by usage of "30pin for all" (later I searched also LCSC for matching alternatives and was shocked how cheap are there, ya...)

But these MOLEX sets are quite okay as reference, so I decided to make my bus this way and took action and ordered few from mouser (here in CZ usually simpler than digikey, as they deliver by fedex during max 3days or so and without customs handling, great). So the MOLEX connectors and matching LCSC items are here:

MOLEX / Connector                        DIGIKEY 1/100 (#)    MOUSER 1/100 (#)     LCSC PART 1/30 (#)
---------------------------------------------------------------------------------------------------------------
78787-3054 backplane socket straight     $1.55/$1.09 (2332)   $1.54/$1.08 (2678)   C2906083 $0.34/$0.26 (2402)
87264-3252 board-board socket(32) right  $4.82/$3.38 (1048)   $4.33/$3.05 (2671)   C2833919 $0.78/$0.59 (776)
87760-3016 card/board header right       $2.68/$1.89 (9567)   $2.63/$1.70 (2272)   C2906021 $0.31/$0.25 (2405)
87833-3020 card header shrouded right    $3.90/$2.73 (3658)   $3.83/$2.69 (1406) 

I read deeply here about RCBus design effort and great result, but I had in mind the smaller 3V3 solution for my local experiments for long time before that (dont have enough cases/examples for cards though). Simply I wanted to connect some more modern chips with parallel bus even to older CPUs, but also to newer MCUs too. So I already stated, I am not pure retro guy, probably ... :-(

here are some simple facts about thing I called finally "7xbus":

7xbus - 2mm/2mm pitch connectors, 2x15=30pin for volume orders (molex board socket found only as 32pin)
7xbus - 30 or 60 or 90 pin card to backplane or board to board (optional) connections
7xbus - 3V3, single sided SMT, hotplate/preheater + hotair (THT connectors mounted manually as last step)
7xbus - possible DFM PCB-fab mounted SMT modules in volume? (THT connectors mounted manually as last step)
7xbus - primarily CPU+MEM module integrated, maybe even with few backplane slots, so NO board-board needed

Dont have started yet to specify pinouts and layouts/sizes, as here ARE for sure many of far more experienced REAL engineers, I never worked professionally in this area, sadly ...

Its not something related to big business, I am only playing myself as the "garage shop" with all the vintage and utopic consequences these days ))

Not to mention my strategic goal of "trying to push" virtual 32bit processor VMEX and his companion high-level assembler ASLIX (both "slightly related" to RISC-V, RV32EM specifically, with optimized decoding) for simple embedded things and playing with something portable to compare performance of different systems and learn assembly-like development of simple software - unified way

(this MAY be highly controversial for FAST native machine code lovers, I agree, but i treat this is something like "new basic" as I am still working on specs and reference implementation). Finally, there can be pure native implementations done by native target experts, OR semi-native ASLIX compiled engine/runtime using "as-portable-as-possible-approach" at the source level + of course totally portable code targeting VMEX. And that semi-native ASLIX way of coding things for native targets drivers is considered too.
(Many thanks for all people from Z80Retro! community who helped me to test this in CP/M)

Its all only sets of ideas in wild ... trying to simplify complex things down back to "assembly with human face";

https://github.com/apws/230326-VMEX

... appended are some preliminary pictures related to that smaller 3V3 "7xbus"
... plus CP/M vmex.com (preliminary, tests only) and ISA/OS drafts

If anyone interested, I will be pleasured to cooperate. Peace;

Petr

[Bill Shen]

I thought 2x22 2mm connectors (male, female, straight, right-angle) are quite cheap and readily available.  I have bagful of 2x22 2mm connectors, male & female,  for various projects.  They are around $0.25-$0.35 each in quantity.  A standard 1.6mm thick pc board straddle 2x22 2mm connector so it can solder directly to pc board with 2mm spacing finger pads on both side.   You can have a backplane made of 2x22 2mm straight female to accept pc boards with 2x22 2mm SMT finger pads that has 2x22 2mm straight male soldered.  (I'll probably get banned with any more of this straight male/female talks !!)

I don't know of backplane made of 2x22 2mm connectors, but I myself and others have backplane made of 2x25 2.54mm connectors.  They are also quite inexpensive and readily available.  I think the 2.54mm connectors are more rugged and easier to align and plug in.
  Bill

[Mark T]

1.27mm pitch 1x40 bent male connectors and straight female connectors are also available, so you could build a 1:2 scale RC2014.

I have been playing with smt components on 1.27mm pitch proto board recently. PLCC44 z80 on point to point wired module to 1x40 1.27mm pitch, plugged into an adapter to 40 pin dip z80. Moving back to 2.54mm pitch is like heavy engineering. 30awg wire is a bit heavy, 34awg seems about right.

1.27mm pin headers have 0.4mm x 0.4mm pins. If you remove alternate pins these can be used to plug into dip sockets and don’t open the contacts as much as the round pin headers that are normally used.

[7alken]

yeah, very interesting too :-) ... and btw, I am quite fascinated(!!) by your edge straight 44pin CF-card adapter speciality - you are using it even without soldering as momentary/temporary (no breath) connection?? these straight male/female talks are nice :-) 

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[Bill Shen]

1:2 scale RC2014, LOL!!!  (I don't know why it is so funny, but it just is).
34 awg wire sounds interesting.  Is it insulated and where do you get a roll of it?
  Bill

[Bill Shen]

This is how I plug SMT CPLD in solderless breadboard.  The small pc board has 22, 2mm spacing finger pads on each side.  It slides between a 2x22 2mm male connector (notice it is not soldered but the contacts are good), then plug into an expander board to 2.54mm spacing and straddle the solderless breadboard like the standard 300mil IC.
  Bill

[7alken]

hi Mark, ya, I was searching recently on digikey/mouser for 1.27mm too, but was unable to find there matching sets available, and its really too tiny, while what you sed about removing odds is interesting too - btw exists some chinese shop with similarly good selectors as digikey/mouser ??

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[7alken]

yeah Bill, as I sed, fascinated :-)

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[7alken]

Bill, definitely, I forgot for this, added this line to the table - straight square pins, with STANDARD board thickness (1.5mm) it fits and HOLDS on board FIRMLY;
(this way in fact only 2 types of straight cheap connectors are okay for almost everything ...)

87758-3016 card/board header straight    $3.08/$2.16 (6018)   $2.71/$1.89 (1875)   C6332229 $0.11/$0.08 (7120)

the straight example picture shows my 30pin squared pins connectors bound to standard thickness board, here SDIP64; all 2mm squared spacings can be firmly fitted on over the board edge ... only the straight socket uses "flat" solder pins and this one DOESNT hold firmly, there is say 0.2mm space, but its solderable this way too...

this may require different planning of double-sided card layout, but in case of RCBus adapter it in fact provides direct insertion to THT connector on RCBus, while THT connector on card will have NON-FLAT back side ... its also true that soldering of this on card is even easier than THT close pins

thanks for this

[7alken]

also, its fact these 44pin are very nice, ... I only cant get quickly cheap ones (and right angle) from mouser; that LCSC is in fact very nice selector too, btw;

[Mark T]

I used aliexpress for 1.27mm protoboard and header pins. I think LCSC also have the 1.27mm header pins. There seems to be two styles. 1x40 type arrived as 1:2 scale of the 2.54mm pins. I tried ordering more of the same but received a different style 1x50 type. I prefer the 1x40 style to create adapters to dip sockets. Using the 1.27mm proto board to hold the pins straight as the plastic is sensitive to soldering temperatures.

I tried using enameled wire, but the temperature to solder through the enamel is a bit high and ruins the small point soldering tip quickly. The 0.8D type tip seems to work better at 1.27mm pitch. Most common wire wrap wire is 30 awg pvc insulated, the insulation tends to shrink back when soldered. The UL1423 type with PTFE or PVDF insulation handles the soldering better and available in 26 awg to 38 awg. I bought a range of samples in 5m lengths. 38awg is difficult to strip without breaking, Its expensive for full reels.