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A little something I'm working on right now..

P

PacMan

Experienced Member
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Nov 13, 2008
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Sweden
I was having trouble finding a serial board for my Altair at a reasonable price so I decided to build my own board. Here's a picture of it in its current state.

s-100-lab-mounting.JPG


The 40-pin dipper is a SCN2681A DUART, which is a great device to work with. It's still missing the transceivers but that is coming along.

When I started to make the schematics I also decided to put in a socket for an EPROM (or as in this case a flash memory). I also opted for a two PLD (16V8 ) decoding and bus control solution. The EPROM is selected by the LS85 and the DIP switches to the left in the board.

Later I plan to add a floppy controller to the empty upper right section of the board (notice the conveniently placed 34-pin connector), but that is for another rainy day.

The 2681 has a 8-bit output port and a 7-bit input port that will be used to (among other things) control the /PHANTOM signal to be able to disable the on board EPROM if I should ever want to run CP/M on with this board.

/Pac
 
Hi! Nice! Where did you get the prototyping board? It looks new. Did you design it yourself?

Excellent job! Thanks for sharing!

Andrew Lynch
 
Hi! Nice! Where did you get the prototyping board? It looks new. Did you design it yourself?
Click to expand...

Yes, I designed it during the christmas holiday and got it here about a week ago. I will be making a small batch of them shortly, if you want one let me know.

They carry two 5V regulators and one +12 V and one -12 V regulator and a bunch of decoupling caps. Originally I wanted to place as much generic logic on the board as possible but then I found myself locked into an 8-bit card without the possibility to do a 16-bit card. Instead I made the lab board as simple as possible including only the voltage regulators.

/PacMan
 
Heya PacMan,

I've got a Tarbell 2022 and a CCS 2422 - both use the FD1793B.

You've got first dibs 'cause you asked, but they are generally available if you don't want 'em.

I can keep digging if you'd like. Those were from a more accessible box of S-100 cards. :)
 
Hi Pacman! What did you use to design the prototype board PCB? KiCAD, Eagle, or ? I am big fan of KiCAD although there are lots of good EDA packages these days. You can't argue with KiCAD's price though!

Thanks and have a nice day!

Andrew Lynch
 
Andrew,

This board was actually done with KiCAD. It was my first board using this CAD package and I must say that I am impressed with it. I can mention (but i wont ;-)) several packages that costs thousands of dollars that is no better than KiCAD.

/Pac
 
Hi! Thanks! I thought I recognized the layouts. Are the schematics and PCB files available? You are free to post them on the N8VEM wiki if you'd like.

I am quite impressed with KiCAD as well. As a free tool, I kept my expectations in check but so far it can do everything I have wanted it to. The program continues to evolve and smooth out the rough edges too. Add in FreeRouting.net and it is a impressive combination!

One project that's been in my mind but never come to the forefront is a ECB to S-100 project. I have a circuit in a book that shows how to map the Z80 signals to S-100 boards and from there its a short leap to ECB. The book is called "S-100 and Other Micro Buses" and has the circuit in the back.

It seems to me a small ECB and S-100 motherboard with the necessary interface logic would allow an N8VEM SBC to control S-100 boards. However the complicating factor is not the logic interface because that's quite simple. Its the S-100's power supply requirements.

Here is a half thought out idea I've been bouncing around in my head recently to address the situation. Please let me know what you think of it...

I was sorting through some old PC scrap stuff and found some old Dell laptop power supply bricks which I thought might be useful. Instead of a straight linear S-100 power supply, how about using a couple scrap PC laptop bricks; one for the +20 VDC power rail (nominally +16v but I've seen this range quite a bit and 20 VDC is probably in the tolerable range) and run it through a 7808 or similar for the +8 rail? Use the other Dell laptop brick "flipped" to supply the negative rails in a similar configuration. I am not sure if the laptop power supplies would have the current capacity sufficient for more than a card or two. It might for a small S-100 motherboard system though. That would be perfect for home brew hobbyists.

Of course, replace the proprietary connector and replace with something more commercially available like something from MOLEX.

These are just speculations and I don't know how practical it would be. If there was an easy and cheap fix to the S-100 power supply situation that did not require a full blown linear or tweaking the internal circuitry of an ATX power supply I think small S-100 systems would be more practical for home brew hobbyists. I have various S-100 boxes like NorthStar Horizon, VG, and other home brew S-100 systems but they all are *large* units and require a lot of space to work on. ECB is *much* more compact and a lot more hobbyist friendly in many respects, IMO.

Thanks and have a nice day!

Andrew Lynch


PS, I re-read my post and I accidentally mangled the paragraph on the power supplies when writing it. I've revised it to say what I meant; one PS brick would supply the positive rail (+20v, and through a 7808, +8v). The other PS brick would be reversed to supply the negative rails (-20v, and through a 7908, -8v).

The neat thing about using the Dell laptop supplies is that they are very cheap on eBay. You can see used models of PA-6, PA-9, PA-10, PA-16, etc for $5 or less. Get any two of those, add a couple of 8 volt regulators, and you can form a simple low cost S-100 power supply. It won't have much capacity but enough for a couple boards.
 
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Andrew,

It sounds like an interesting idea to build a ECB <-> S-100 interface. It would give you access to a lot of interesting S-100 functions. With that said I might add that I have found that S-100 equipment is getting more and more difficult and expensive over time. I have been trying for some time to find a floppy disk card for a reasonable price but most boards start at $100 and with shipping I often land upwards $130-$140 which is ridiculous.

Anyway, power supplies.... I always use good (yes expensive) switch mode power supplies when I work on equipment that need more than on or two different voltages. In the past I have spent to much time debugging hardware (and software) that was behaving incorrect due to faulty (or badly designed) power supplies. The power supply is as important (or maybe even more so) as the hardware that you are designing, building or working on.

I remember specially one episode where I designed a 8051 based system (only the MCU part) for a customer. The design worked according to the specification when it was handed over to the customer (using our internal lab power supplies). Months later when they were integrating our boards into their product nothing worked as expected. I was called in to "fix our faulty design" and ended up spending about a week trying to find the problem. In the end it turned out that their inexpensive power supply solution was causing all the electronics in their system to malfunction.

Lesson learned, don't skimp on the power supply ;-)

You should select something like this http://www.meanwell.com/search/rq-125/default.htm to work with. The +-15V is perfect for S-100 system and the +-5V can probably be jacked up to +-7V without problem which is also perfectly okay. I could not find a supply with those exact specs on ebay right now but I have bought several of them in the past so I'm sure there will be more. The last one I bought was $10 for a 150W +-12V and +-5V which which I turned up to +-15,5 and +-6,5V. Quite sufficient for a few boards.

/Pac
 
Hi! I like the dedicated power supply approach definitely! It really would simplify the PCB and probably reduce one side by 4 cm or so since the LM317/LM337's wouldn't be needed.

The N8VEM ECB backplane fits on a Eurocard 160x100 PCB and has 6 DIN 41612 connectors. The circuit in the book would probably take (I am guessing) about 12 20 pin DIP chips to implement. That would require probably about 4 x 16 cm area to place and route in a decent manner.

Assuming 3cm centers on the S-100 boards, to add 3 (maybe 4) connectors would require about 9cm or so. I am imagining a PCB of about 16 x 23 = 368 cm2 area (6"x9") or 54 in square. Thats a big PCB but not huge.

Add mounting holes for stand offs and skip the case and that's a low cost S-100 hobby system ideal for prototyping. It'd probably need a switch and a PS connector but the N8VEM ECB backplane already has that in its design. Since it is multiple input voltage though it may be worthwhile to just make the PS switchable rather than on the PCB.

Please take a look at the circuit in the book on TRS-80 to S-100 bus. I think it could be readily adapted to ECB as the TRS-80 is a straight forward Z80 SBC. Its a short step from there to ECB.

No doubt such a design would have major limitations with legacy S-100 PCBs but that is not uncommon either. Many S-100 systems are effectively custom due to the numerous variances in S-100 implementations. Staying with a single vendor helps but making a system of mix and match boards gets rather sporty. Making new boards with S-100 prototype boards should work though.

The only issue I can think of right now is that the CPU clock on the N8VEM SBC is 4MHz where the phi signal on a S-100 bus is typically 2MHz. I wonder if that'd matter? The S-100 bus would be short enough to not require termination but long enough to still be useful.

Its an interesting thought experiment if nothing else. This idea has been floating about in the back of my mind for months and every once in a while it resurfaces.

Thanks and have a nice day!

Andrew Lynch
 
Making some progress with my little board.....

Making some progress with my little board.....

I finally had some spare time to devote to my little board today.

Added the serial buffers (top of the board).
090125-1.JPG


And wired the input address buffers to the S-100 connector.
090125-2.JPG


It actually went much quicker than I had expected. I have done quite a lot of wire wrap prototypes in my days but that involved flipping the board a gazillion times to figure out pinning. Not to mention wiring all VCC and GND signals. With my new prototype board power is always available close to the chips on the backside of the board making it a snap to solder power directly to the chip.

I also figured out that I should add X-Y markers on the board like the hand written ones. Makes it very easy to locate a chip on the board from the schematic (provided you have entered markers on the schematic that is :mrgreen:)

I don't know if you have seen it but the holes on this first board are much to small for the pin headers to fit. I probably had a big hole in my head when I selected the hole size. I probably just figured that the IC sockets needed to fit.

Anyway, that's all for today.

--> Andrew, I'll look at you post more tomorrow when I'm lucid again.

/Pac
 
lynchaj said:
Hi! I like the dedicated power supply approach definitely! It really would simplify the PCB and probably reduce one side by 4 cm or so since the LM317/LM337's wouldn't be needed.

The N8VEM ECB backplane fits on a Eurocard 160x100 PCB and has 6 DIN 41612 connectors. The circuit in the book would probably take (I am guessing) about 12 20 pin DIP chips to implement. That would require probably about 4 x 16 cm area to place and route in a decent manner.

Assuming 3cm centers on the S-100 boards, to add 3 (maybe 4) connectors would require about 9cm or so. I am imagining a PCB of about 16 x 23 = 368 cm2 area (6"x9") or 54 in square. Thats a big PCB but not huge.

Add mounting holes for stand offs and skip the case and that's a low cost S-100 hobby system ideal for prototyping. It'd probably need a switch and a PS connector but the N8VEM ECB backplane already has that in its design. Since it is multiple input voltage though it may be worthwhile to just make the PS switchable rather than on the PCB.

Please take a look at the circuit in the book on TRS-80 to S-100 bus. I think it could be readily adapted to ECB as the TRS-80 is a straight forward Z80 SBC. Its a short step from there to ECB.

No doubt such a design would have major limitations with legacy S-100 PCBs but that is not uncommon either. Many S-100 systems are effectively custom due to the numerous variances in S-100 implementations. Staying with a single vendor helps but making a system of mix and match boards gets rather sporty. Making new boards with S-100 prototype boards should work though.

The only issue I can think of right now is that the CPU clock on the N8VEM SBC is 4MHz where the phi signal on a S-100 bus is typically 2MHz. I wonder if that'd matter? The S-100 bus would be short enough to not require termination but long enough to still be useful.

Its an interesting thought experiment if nothing else. This idea has been floating about in the back of my mind for months and every once in a while it resurfaces.

Thanks and have a nice day!

Andrew Lynch
Click to expand...

Andrew,

Looks to me as if it would be smooth sailing for you to make this happen. You could check Grant Stockly's small S-100 backplanes. A tad expensive but very high quality. Together with that kit your ECB card should be able to plug right into your adapter board and voila, instant cofee ;-) Or are you maybe aiming to have the S-100 connectors already on your adapter board ?! In that case you could choose a less expensive connector than the one used on Grants boards.

I don't think the hardware to adapt the ECB bus to S-100 should be to hard to create, depending a bit on how much you are aiming to support on your adapter card. I'd go for supporting the prioritized interrupt lines (VI0* - VI7*), maybe by using a I8259 or even simpler by using a 74LS148 and a 74LS373 or something similar. DMA could be nice but then you are adding a lot of complexity to the adapter card that could be implemented on the ECB bus or on the S-100 bus. I guess some consideration regarding DMA is needed to make the ECB bus talk DMA fluently on the S-100 bus and vice versa.

Regards
/Pontus
 
Hi! I tried to post a reply on this yesterday but somehow it got tossed into the bit bucket. Oh well! This is the TRS-80 to S-100 bridge circuit I was referring to

http://www.hartetechnologies.com/manuals/Unclassified/S-100_and_Other_Micro_Buses.PDF

It starts on page 115, chapter 14. I have the schematics for the TRS-80 model 1, so I am thinking since it is a basic Z80 design itself, is just implement the minimally required TRS-80 circuitry required by the interface along with the bridge circuit. There really is nothing all that exotic there although I am fairly sure the compatibility of the bridge circuit with S-100 is probably quite limited.

http://incolor.inebraska.com/bill_r/trs80_schematics.htm

The main issue I see with a S-100 design of any sort is the procurement of the female card edge connectors. Certainly they are still available but they are quite expensive. Availability of connectors was one of the deciding factors, along with PCB cost, in going with ECB on the N8VEM design since the connectors (DIN 41612) are inexpensive and commonly available.

Please take a look at the bridge circuit and let me know what you think of the proposed approach. Does it sound reasonable? Do you think there would be interest in such an odd hybrid? For home brew computing, ECB is/was popular in Europe and S-100 is/was popular in the US. The design has the potential to leverage what remains of both hobbyist communities and resources.

Thanks and have a nice day!

Andrew Lynch
 
Andrew,
I glanced through the schematics and they look okey. What I would do is to check out the schematics of a few Z80 S-100 processor boards to see how they have solved the S-100 compatability issues. And as i mentioned earlier you might want to support the interrupt scheme available on the S-100 bus which would make many more S-100 boards run properly in your system.

The connectors are available from Digikey, they have a few different version in stock but the one from EDC (http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=EDC346102-ND) seems like a good choice. It's around $7 if you buy more than 10 of them. I recently bought a set of Sullins connectors for an original Altair 18-slot motherboard but those buggers cost me a little over 16 bucks each, which is a little steep even for me.

I actually have no idea if this kind of board would be interesting. Me, I was raised with S-100 computers s I have a strong link to them and love to play around with them but I don't know how many people that share that sentiment.

It would certainly be fun to do it and I could be willing to help out with testing and some funds if necessery.

/Pacman
 
Thanks! That is exactly the information I was looking for. Right now the how ECB to S-100 bus bridge project is just a thought experiment. My next step is to write up a schematic in KiCAD and post that for some comments.

On the N8VEM project, I am working on Zilog Peripherals board at the moment which is taking up all my time. The CTC and dual PIOs seem to work fine but the DART is giving me fits. I am not familiar with the DART/SIO way of doing things so I don't know if I am initializing it properly although I am able to get the DART to respond to simple commands like setting the RTS pin. Still can't get it to send any data out of the TX pins though.

Its great to see other hobbyists willing to make their own computers. I like S-100 and have several systems but it is not very hobbyist friendly IMO. Still, it is a lot of fun.

Thanks and have a nice day!

Andrew Lynch
 
Just let me know if you need any assitance, it really sounds interesting. Good luck with the DART, i have never worked with that chip so I can't help your there.

/Pac
 
Hi! Where did you get the 50/100 pin card edge connector for KiCAD?

Thanks and have a nice day!

Andrew Lynch
 
Andrew,
I created the entire board myself, which includes the connector (as J1). So when I do another S-100 design (o yes, you know they are coming) I will have a predefined board with everything (J1 connector and board outline) in place. The lab-board was a sort of a first step in this process.

I will try to make sure that you get the KiCad design data for this but at the moment I am really (and I mean really) busy with another commercial (this is how I make my money and feed my kids) project.

To keep my sanity though I will continue to make postings about this board so don't hold your breath waiting for it.

What do you know, I may be the next S-100 board king (OK that is kidding, you got to know that) *hehe*

/Pontus
 
PacMan said:
What do you know, I may be the next S-100 board king (OK that is kidding, you got to know that) *hehe*

/Pontus
Click to expand...

You might be surprised, there's prob'ly enough S-100 enthusiasts around that are starving for new toys. Mebbe not enough to feed the kids, but take them out to a nice restaurant occasionally. That prot board looks real nice, perhaps better than any commercial board I've ever seen. I'd buy one, for the right price. Perhaps you could add a logic probe to version 2.0?

--T
 
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Terry Yager said:
Perhaps you could add a logic probe to version 2.0?

--T
Click to expand...

Ok, that sounds interesting, do you have anything specific in mind ?

Right now i'm thinking that I could add support to the board for both 16-bit as well as 8-bit boards by having a CPLD on board as well as all the necessary buffers to make that happen. In that case you would could make a board that would meet the IEE696 standard when it comes to memory accesses. And if that were the case you could easily (if you know VHDL) implement pretty much the entire standard.............

Whoops, what happened there, to much oxygen to my brain :mrgreen:

Sorry 'bout that, i'm back to reality :cool: Please... i'm really interested in what you mean. it's just my brain that is acting out on me (as it always does when I'm listening to Jennifer Rush (OMG am I really that old ??)).

The current board is a simple prototyping board (which has proven to be very useful) but as mentioned it could easily be improved to be more useful to other uses.

Regards
/Pontus
 
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