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Interested in a home brew Z80 computer project?

Hi All,
Last night I was experimenting with replacing the 1Mx8 EPROM with reused Flash ROMs I bought from a board scrapper. I got a whole bag of various miscellaneous chips and it included a number of reprogrammable 32 pin memories.

Unfortunately after trying about 6 different chips, I didn't find any that would work. However, I think with a bit of research I may be able to fashion a "shim socket" to fake out the Flash ROM and convince it to work.

The investigation continues...

Thanks and have a nice day!

Andrew Lynch
 
Hi All,

The 128Kx8 SRAMs arrived today so I will test those out in the machine tomorrow. Its been awful busy here the last couple of days. The orders are coming in and I am packaging up the PCBs and sending them on their way.

I am a bit surprised at the high percentage of people requesting the 1Mx8 EPROM and I guess I did not anticipate that happening. Probably will have to regroup here soon as I will run out of the EPROMs pretty quickly. I have no problem programming the EPROMs for people but getting the actual EPROMs may take a while. I am working some arrangements for additional chips. If I just run out, we can use the 128Kx8 chips in the meantime until I figure out what to do next.

There are a couple of alternatives for the 1Mx8 UV EPROMs. I can order some new ones from Jameco in bulk for about $7 or so. Alternatively, we could use OTP (One Time Programmable) PROMs for about $6. However, either case does exactly what I was trying to avoid... jack up the cost. I put in some RFQs for more parts and we'll see what shakes out. I am not a fan of OTPs for this application since once I burn it for you, that is it. There is no reuse or updating the chip. Of course, then your chip is practically invulnerable and you'll have a "fall back" chip but you'll need a different one if you ever plan to modify the software.

As a not very practical alternative, people could just order the EPROMs, send them to me and I'll program it for you and send it back. That'd work but what a PITA and shipping isn't cheap these days.

I still need to investigate using the smaller FLASH ROM parts with a shim socket and see if that'll help. That'll take a while though as I need to review and compare some datasheets.

Overall things seem to be going OK. I guess we'll see as the first build reports come in. For those with PCBs on the way, please be sure to post lots of photos and progress reports. I am certainly curious as to your progress and maybe we can all help out if anyone has problems.

Thanks and have a nice day!

Andrew Lynch
 
Hi,
I was able to get a few more 27C801s so that should solve the immediate EPROM availability problem. Still looking for more parts though so if anyone has any ideas, I am open to hear them out.

Thanks and have a nice day!

Andrew Lynch
 
Hi All,
I tried the 128Kx8 SRAMs and they did not work as direct substitutes for the 512K SRAM part. It is probably a similar same problem as with the 29Fxxx Flash ROMs substituting for the 1M EPROM.

Using shim sockets, I'll have to make some adjustments to the circuit for these alternative parts to work. Given the price difference between new 512K and 128K SRAMs is only about 50% and less than $10 it is hardly worth it once you figure in the cost of the 32 pin socket and time necessary to convert it. Still, it is a possibility and I'll continue investigating some lower cost options.

If anyone has other ideas for cost reductions please let me know. Thanks!

Andrew Lynch
 
compiler/assembler

compiler/assembler

I am looking for a compiler/asssembler that will take Z80 to TMS9900. There was a z80 chess machine that was converted to run on the TI 9900 CPU so I suspect such a program exsists. Any help would be appreciated. thank you
 
Hi,
After some investigating, I have found how to make shim sockets to allow 29F020 style Flash ROM chips to work in the SBC. I have about two dozen of those (256Kx8) gotten from scrappers "throw aways". They are not the full compliment of ROM but are large enough to put in all the N8VEM software to date and still have about 50% remaining capacity.

You'll still need a programmer to change them but not an eraser to reuse the chips. The SBC does not support in circuit reprogramming although that is a possibility with cuts, jumpers, and some software writing. I am not planning on doing it but maybe someone will desire Flash ROM sufficiently to make the changes. They are fairly simple modifications at least in theory. :)

Thanks and have a nice day!

Andrew Lynch
 
N8VEM SBC BOM/Parts List

N8VEM SBC BOM/Parts List

Hi

Some people have requested a BOM/Parts List for the N8VEM SBC so I posted one on the N8VEM website files area. Feel free to use it but please first read the post in the discussion forum on the subject.

Thank you in advance and have a nice day!

Andrew Lynch
 
Hi,
So far things are going OK with the SBC PCBs. People have received their boards and there have been no major problems yet.

After a bit of research I found that 27C4001 EPROMs (512Kx8) are suitable replacements for the 27C080/27C801 EPROMs. They are half the size but cost somewhat less. Its probably not worth the substitution if you are building your own SBC and buying the parts but its useful to me if my supply of 27C801s runs out. I can easily buy the 27C4001's from the used surplus market at a reasonably low cost.

One thing I did want to mention is that if you are building your own SBC, be sure to use machined pin sockets for the EPROM socket. Most likely that socket will be the one with its chip removed and replaced. You'll want a tough and durable socket there if possible. A ZIF would be better but I don't think the clearance will allow it. I tried with one of mine and the filter capacitor is in the way. That'd easily be removed with no problem but if its already soldered in its probably not worth it.

Please let me know if anyone has any more questions or thoughts on building their own home brew Z80 CP/M computer.

Thanks and have a nice day!

Andrew Lynch
 
Hi All,

Some people have received their PCBs and are busily working on getting their SBCs working. There are some really nice projects out there and a couple of really great photo albums out there documenting the build progress.

I liked these photos so much I thought I'd share with the nice people here. If these pictures don't get you motivated to build your own home brew Z80 computer, check your pulse!

Seth's very nice looking build:

http://www.flickr.com/photos/twylo/sets/72157605637029141/

Seth's doing a great job! Nice Panavise too. I think I want one of those...


Tony's doing great too!

http://s117.photobucket.com/albums/o62/nurb432/Z80 Project/

Sweet looking case... Check out the passives and the 2N2222A TO-18 transistor installed...


I am glad to see the projects moving along and can't wait to hear those first test results.

Great job guys and please keep us posted on your progress! I will be glad to help out in any way I can.

Thanks and have a nice day!

Andrew Lynch
 
Hi All,

There is some good news on this day...

Seth got his N8VEM SBC kit working! Here is the link:

http://groups.google.com/group/n8vem/t/1ba82bc54a81d858

Apparently he posted some photos on Flickr as well but I can't see them from here.

So for all you waiting to see if this SBC actually can be built and will work in someone else's hands, here is your proof! The Z80 home brew SBC project is alive!

Yippee! Much dancing and rejoicing!

Seth added some of his own personal touches to his build and that is nice. The SBC is meant to be customized and include personal variety. I am always surprised at the innovative and different ways people come to do things. That is really good and I am very happy it is now his unique creation. I would like to encourage all of the SBC builders to get theirs working and do experiments with them. Customize, Explore, Innovate!

Hopefully this will drum up some interest in home brew computing. Thanks and have a nice day!

Andrew Lynch
 
Ok, people, if you're building this SBC and need parts, I got e-mail from a place today that deals with parts and checked it out.

They have almost everything you'll need, sockets, chips, resistor, caps, etc.

They have a 20 buck minimum, BUT if you need A resistor, you can order A resistor instead of having to take a bag of 100. I think the only major chip they didn't have was the SRAM, they even have the EEPROM.

Prices are good and I'm not affiliated with them in any way.

www.unicornelectronics-nospam.com (remove the -nospam, of course)
 
Hi,

Thanks Richard! I can vouch for UnicornElectronics. I have dealt with them quite a bit and they are good guys. They deserve our support and have some pretty unique and special stuff. Please consider them for your electronics needs.

Personally, I have never had any trouble with the $20 minimum since it is like a kid in a candy store whenever I go to their website :)

Thanks!

Andrew Lynch
 
Hi All,
Well, the good news is the SBC PCB is selling and my stock is moving.

However, if you are waiting to order your PCB I recommend you do it soon. I have passed the 50% left mark on remaining stock and the end is near.

Please contact me if you would like to order a PCB. I do not know if/when there will be another run. If there is one, it will be weeks away as it takes about three weeks from order to delivery to me. Shipment to you is on top of that.

Thanks! Have a nice day!

Andrew Lynch
 
I get most of my project parts from Unicorn. I highly recommend them.
 
Hello Andrew,

I don't know where I should post this, but for the sake of consistency,
I go ahead and post it here :) !

I have always had this question about handshaking procedure for
terminal emulators; some SBCs use only null cables and some
others use standard serial cables. Would you please explain about
the handshaking procedure for an emulator such as Hyperterminal?

Thank you very much

ziloo
 
Hi!

There is a similar thread on the N8VEM discussion board. Seth was able to get his SBC to work using his serial cable like this:


[N8VEM -------- 9-pin DSUB]
2 (DSR) ------- 4
3 (RX) ------- 3
5 (TX) ------- 2
7 (DTR) ------- 6
9 (GND) ------- 5


Seth posted photos of his serial cable so you can see it up close.

http://groups.google.com/group/n8vem/t/8730736c05641986


My cable is a bit different since I am using HyperTerm and like to use hardware handshaking.

PC DB25 (9 to 25 pin cable) SBC (25 pin female)
2 TD----------------------RD
3 RD----------------------TD
7 GND---------------------GND
6 DSR---------------------DTR
20 DTR----+----------------DSR
5 CTS----+

It is the same as what you have except pin 20 DTR and 5 CTS are wired
together. This allows hardware handshaking using HyperTerm.

As to whether it is actually using hardware handshaking is probably a
matter for debate but at least it doesn't hang anymore...

Making serial connections between computers, especially the older ones, is a complicated subject. I can usually make something work with a RS-232 breakout box but I am no expert on the subject that is for sure. I like to use hardware handshaking whenever I can but sometimes it isn't an option.

Thanks and have a nice day!

Andrew Lynch

 
Yeah! Success! Huzzah for our very own Rich Camarda! He built his own SBC and it is working!

SUPER JOB RICH! CONGRATULATIONS!

Much dancing and rejoicing by all!

:)

That makes two SBCs in a row working. There may be more out there I don't know about yet but who knows?

You can see the announcement and photos of Rich's shiny new SBC at:

http://groups.google.com/group/n8vem/t/c95b46cbbc5c1596

http://n8vem.googlegroups.com/web/N...Vb2G1qiJ7UbTIup-M2XPURDRRxzGhO7K7sGg6P-gotD4g

http://n8vem.googlegroups.com/web/N...Vb2G1qiJ7UbTIup-M2XPURDTrvnQmBxuwO1h4UOLczkXq

Thanks Rich! BTW nice touch with the Red LED and the Wyse terminal. That is some retro cool! Enjoy your SBC!

Have a nice day!

Andrew Lynch
 
Hi All,
Well, good news and bad news.

The good news... The SBC has been more popular than I expected. Originally I thought maybe there would be 10-12 interested people. I had enough PCBs to cover all of them and some extras but many more people have come forward recently. I think the photos of Seth's and Rich's working systems are encouraging people to take the plunge and also there isn't much much like it right now.

The bad news... I sold out of all my PCBs.

I have plenty of EPROMs (I think) and the website seems to be going OK. Overall I am pretty happy with it.

I would like to order another batch of PCBs but before I invest a bunch of $$$ I'd like to measure interest. I really cannot afford to spend hundreds of dollars on a box of PCBs only to have them sit unused. There has to be a method to mitigate the risk so I am trying a new approach.

I start a waiting list for interested people with a firm commitment to buying the PCB when they are available. It will be several weeks, at least three from the time I make the order plus delivery. If and when the waiting list gets big enough to make it viable, I will make the PCB manufacturing order and distribute the PCBs to those on the list first and then make the rest available to whoever else wants them. The deal is the same as before.

If you are interested or have other ideas please contact me or reply here.

Thanks and have a nice day!

Andrew Lynch
 
I may be interested in one or a couple (2-5) boards. To summarize: are there a lot of components one needs to gather yourself, or do you offer kits of the required parts as well as the boards themselves? I suppose the most basic resistors, diodes, capacitors and so on are easy to find locally, but in case there some more specific items it is good to recapitulate this.
 
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