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Interested in a home brew Z80 computer project?

Just to second what Andrew has said, tonight I built two. As in two complete CP/M machines with a keyboard and a small LCD display and the ability to run CP/M programs. And a big thankyou to the hoster of the Walnut Creek CP/M archive. It is a treasure trove, though it takes a bit of searching. But I found what I needed, which was a small MBASIC program that can chain a .sub file. So now it is possible to daisy chain programs. All the parts for wireless CP/M networking are falling into place, and this ought to have real applications for networking vintage computers too. Can already send any file wirelessly over many hundreds of metres using xmodem. One project coming to fruition is a router based on the N8VEM that can route wired and wireless RS232 signals.

The Propeller monitor is also taking shape. One of the builders has suggested that the N8VEM is too quiet and he has suggested the Propeller terminal have a speaker and produce sound effects of disc reads and writes? Maybe someone could record a .wav?
 
BTW Z80 and CP/M are just the local favorites and not a mandate. If you want to make your own SBC using your favorite CPU to run that free OS you've been dreaming about you are welcome to use the N8VEM system as a platform for your development. For example, I would *love* to see some of the 6809 and/or 68K gurus find a nice home for their OS-9 with the N8VEM project. You are certainly welcome and you can use the Z80 SBC as your IO processor!

Thanks and have a nice day!

Andrew Lynch

PS, just an example; take a design similar to one of these EPAC 68008 and mount it on a Eurocard with a 8255 to act as the communications link between the 68K and the ECB. Write a N8VEM SBC application to serve IO requests to the 68K via the 8255. Instant home brew 68K with peripherals!


I' d like to see an interface to this board, if anyone is interested:

http://www.users.cloud9.net/~stark/sbc02.htm

It's a kewl lil' gizmo, very simple to build, that runs a tiny version of BASIC, but no mass storage.

--T
 
Hi Terry! How about one of these on an N8VEM ECB prototyping board.

Hook the 6821's parallel IO a 8255 parallel IO (8255 only needs an IO decode 74LS32) That's 5 chips by my count.

There would need to be Z80 software on the N8VEM to serve IO to the 6802 via the 8255 and corresponding software on the 6802 side for its client IO.

Do you know of any 68xx hobbyists that'd be interested in pursuing such a creature?

I would really like to broaden the appeal of the N8VEM to other home brew computer hobbyists. Maybe making a 68xx device would be appealing to them?

This sounds interesting.

Thanks and have a nice day!

Andrew Lynch

PS use 8255 mode 2 for bidirectional IO via port A and port C for strobe pins. Not sure what the 6821 can do but probably IO on one port and control on the other.
 
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AJ,

Brilliant! Gotta have one...but that's a whole 'nother project to add to my queue. Still looking to find a good use for my SBC-2, although your interfacing ideas look doable, as it uses a 6821 as well.

--T
 
Please be sure to let me know if there is anything I can do to help your group with their build of the SBCs.
Yes please. I've located the parts lists and tried to figure out what parts are mandatory, which are recommended and which are additional.

I found this list which has all the items that can go on the board. Furthermore I found this page where you have taken a stab at building the cheapest possible SBC, leaving out a number of components. I also found some tutorials like James Moxham's and Oscar Vermulen's. James writes he left out the clock chip while Oscar clearly didn't install the 96-pin DIN 41612 connector which I believe is for connecting the board to the ECB bus?

On the step by step page, it says a parts list should be uploaded by July 5th, 2008. Probably it was, just that I find it a slight bit hard to follow. I'm sure these questions have been brought up in your mailing list, but I'm too lazy to search through it, in particular as you have a complete parts list already listed.

Some of us in the group would hesitate in spending too much money on something they're not sure what they can use it for, thus I'd be very thankful if I got some pointers and tips what is a good cut-off point on parts required, parts recommended and parts that can be added afterwards. I see that members of the group have made a lot of interesting additions that we may partake in at a later stage, but the first part would be to get the basic boards running through a serial connection I presume.
 
Yes please. I've located the parts lists and tried to figure out what parts are mandatory, which are recommended and which are additional.

I found this list which has all the items that can go on the board. Furthermore I found this page where you have taken a stab at building the cheapest possible SBC, leaving out a number of components. I also found some tutorials like James Moxham's and Oscar Vermulen's. James writes he left out the clock chip while Oscar clearly didn't install the 96-pin DIN 41612 connector which I believe is for connecting the board to the ECB bus?

On the step by step page, it says a parts list should be uploaded by July 5th, 2008. Probably it was, just that I find it a slight bit hard to follow. I'm sure these questions have been brought up in your mailing list, but I'm too lazy to search through it, in particular as you have a complete parts list already listed.

Some of us in the group would hesitate in spending too much money on something they're not sure what they can use it for, thus I'd be very thankful if I got some pointers and tips what is a good cut-off point on parts required, parts recommended and parts that can be added afterwards. I see that members of the group have made a lot of interesting additions that we may partake in at a later stage, but the first part would be to get the basic boards running through a serial connection I presume.

Hi Anders! Thanks! Yes, the parts list/BOM has been a bit of a controversy. The issue is that there is not just one parts list. There are several and in fact many different builder styles and implementations result in a large array of potential methods to build. The good news is practically everyone I have heard of has worked AFAIK. Some use the Digikey parts list, others the Jameco, others you can't tell them how to make their SBC and they'll do it whatever way they please! That's great since home brew computing is all about personal expression and the differences are welcome!

The issue of how to make the least expensive SBC has come up several times. My suggestion is that if you'd like to pursue a low cost option is to just start building using the minimum required parts list and have your test equipment standing by to test as you go. Leaving parts off will result in lower cost but there is a risk of leaving off a part you'll need. About half of the parts can be safely left off. The things that are necessary are the CPU, ROM, UART (for serial communications -- even this is optional if you are willing to use an oscilloscope), and some of the glue logic. The rest is optional. Operating an SBC without RAM sounds odd but it is certainly possible and there are debugging programs included which do that exactly.

Certainly, the ECB interface, bus buffers, the RTC circuit, the PPI, much of the memory paging logic (MPCLs), can be safely left out without compromising basic functionality. However, when you do want to use them obviously you are going to need them installed and working.

I suggest just writing up what you think you want to do and a parts list and then posting on the mailing list for comments. The N8VEM builders are a friendly and helpful group of people who will jump at the chance to help out.

I hope this helps! Thanks and have a nice day!

Andrew Lynch
 
Hi All! I just received a new batch of SBC PCBs so there are *plenty* available if anyone would like to get one of their own. I have all the PCBs and everything is available. So far there are five PCBs:

N8VEM SBC (Z80, CP/M, RAM/ROM drives, UART/PPI/RTC)
ECB backplane (6 slots w/switch and PS interface)
ECB bus monitor (like Jade Bus Probe but for ECB)
ECB prototyping board (make your own peripherals, rapid prototyping)

and the newly arrived:

Disk IO board (IDE and FDC i8272)

All the boards are available for $20 plus shipping which is typically $2 in the US and $5 overseas.

The Disk IO board is fairly new still so the software is not fully mature however there are several builders with Disk IO projects underway so I think we'll see new developments soon.

I have a Zilog Peripherals board (CTC counter timer, DART dual serial ports, and dual PIO dual parallel ports -- four 8 bit ports total) in development now. There is a hardware prototype going into test fairly soon. No estimate for when that will be available. There a lots of other ideas in varying states of detail for other follow on peripherals but I won't be taking on any new projects until the Zilog Peripherals board is completed.

If you are interested in building your own home brew computer, just join us on the mailing list and/or contact me directly.

Thanks and have a nice day!

Andrew Lynch
 
Hi All! Its been a while since my last update but lots of things are developing for the N8VEM project. If you are interested in making your own home brew Z80 CP/M computer now is a good time to start. I have lots of PCBs for all the N8VEM components; the N8VEM SBC, the ECB backplane, the ECB bus monitor, the ECB prototyping board, and the Disk IO boards are all available and ready to go. All boards have been built by N8VEM builders and are in varying degrees of operation. The Disk IO is the most recent and probably the least mature but even it is getting a work out recently.

Whats new? Well, the N8VEM Zilog Peripherals board is almost finished in the trace optimizer, I think. It is nearing completion and as soon as its done, I will make a PCB manufacturing order. It brings a system timer, dual serial, and dual parallel IO in the form of a Zilog CTC, a DART, and two PIO chips.

Next is a 6809 "host processor" which is basically a 6809 SBC on an ECB prototype board. It communicates with the rest of the world via a parallel interface to the N8VEM. It uses the Z80 SBC as its IO processor so the 6809 is free to do what it does best with minimal interference from a IO cluttering up its memory space. I just got the prototype running on my bench and once I get some software and the 6821 to 8255 interface working it will be made into a manufactured PCB like the rest of the N8VEM components.

Some of the builders are requesting an ECB bus extender so that will follow the 6809 host processor. I am also working on an S-100 bus bridge and S-100 backplace project for the N8VEM but that is quite a ways off. However, the S-100 backplane plans are posted in the N8VEM wiki if you'd like to see them.

There are a number of other projects in work as well. Dave is working on a Propeller IO board which should be neat. James is working on a massive wireless mesh project that is just incredible in scope. You'll have to get him to explain it though since it is fairly complicated. Bill is rewriting the N8VEM SBC ROM to make it better with a much improved CBIOS and CP/M. Rich, Rich, and Max worked quite a bit on the Disk IO board IDE section so that is working. Really there are many things going on and this is just a partial list of what I can remember right now. No offense intended if I didn't mention someone's project but there are so many builders pursuing so many different directions at once I get confused as to who is doing what.

Also there are couple of side projects of note not necessarily N8VEM but related. Bob is selling a Z80 ICE circuit which has gotten some good reviews. I bought one and its sitting on my bench staring at me waiting for its turn on the bench. Vince is now selling his PockeTerm terminal replacement controller which is/was codeveloped with some N8VEM builders. I have a couple and am looking for a chance to build them soon as they are very nice using a standard PS/2 keyboard and VGA monitor for a serial terminal.

I intended this message to be short but so much is happening recently its just a very exciting time. If you are interested in joining the N8VEM home brew computing project feel free to stop on by the mailing list and/or wiki and join in the fun. You don't have to build your own system but I think you'll want to as it is a lot of fun. Every builder who has tried making their own has succeeded as far as I know. At least I don't know of any out there which haven't worked after a little work. Most work on the first try so it is an ideal starter project. With the new software development it is even more friendly to new builders.

Thanks and have a nice day!

Andrew Lynch

PS, I uploaded a couple of fuzzy pictures of the new 6809 host processor prototype to the wiki in the m6809 folder. It is working and running a couple of small diagnostic programs as of tonight.
 
new and interested, hello all!

new and interested, hello all!

I found this thread and joined the forum to participate, if I may. A TRS-80 Model III was my second computer and having recently begun working with microcontrollers, I've wondered if it would be possible to build a Z80 machine.

I've been in the software business for more than 20 years so I might be able to help, and I love retro stuff.

Joe
 
We hope to see you over at the N8VEM forum! The N8VEM forum has a lot of discussion about building boards and getting things working. But there is a lot of very relevent discussion on this forum too as these are vintage designs running vintage software. I just built another board this evening - this time a design with 4 serial ports - 1 for the monitor, 1 to a PC, 1 to a radio module and 1 will be going to a real world interface board. Got a LM2575 switching reg too, and finally everything runs cold.
 
I found this thread and joined the forum to participate, if I may. A TRS-80 Model III was my second computer and having recently begun working with microcontrollers, I've wondered if it would be possible to build a Z80 machine.

I've been in the software business for more than 20 years so I might be able to help, and I love retro stuff.

Joe


Hi! Please join us on the N8VEM mailing list and also the wiki:

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

http://n8vem-sbc.pbwiki.com/

Thanks and have a nice day!

Andrew Lynch
 
Hi All! I just wanted to let people know that the N8VEM Zilog Peripherals PCB has now arrived and you can order those. I have PCBs available of everything so if you'd like to build your own home brew computer this is a good time to start. You only need the SBC PCB to start and can optionally expand your system with the other PCBs.

I have PCBs for the N8VEM SBC, ECB backplane, ECB bus monitor, ECB prototyping board, Disk IO board, and the Zilog Peripherals board. There is an active community building their own systems and using them for a variety of things. I recommend joining the mailing list and wiki to see the latest developments and also ask questions to the community.

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

http://n8vem-sbc.pbwiki.com

I've built a prototype 6809 host processor board and its PCB is in work at the moment. No estimate as to when it will be available but several weeks at least. It is just a 6809 processor that attaches to a N8VEM system as a peripheral. It includes an expansion bus to allow builders to customize it as desired.

Please contact me if interested. Either reply to this thread or send me a PM. PCBs are $20 each plus shipping which is generally $2 in the US and $5 overseas. Ordering multiple boards reduces shipping depending on weight. I prefer PayPal but will make special arrangements as needed.

The N8VEM home brew computing project is a completely ad hoc, all volunteer, amateur, nonprofit, noncommercial, hobbyist project. It grows in random directions based on the interests of the builders involved. The PCBs are extra units I was going to order anyway and am making available to the community at cost. There is no long term plan, no formal leadership, no board of directors, and no commercial interests are involved. Basically, if you want something you either make it yourself and/or ask someone in the community to help you.

This is real home brew computing and a lot of fun. You are welcome to participate. I appreciate all the great works builders have done in the spirit of home brew computing. Thanks and have a nice day!

Andrew Lynch
 
Hi All! Just a quick note on some developments with the N8VEM home brew computing project. Things are going well. I have all six current PCBs (SBC, ECB backplane, ECB bus monitor, ECB prototyping board, Disk IO, and Zilog Peripherals board) on hand so if anyone would like some please contact me. James (aka Dr_Acula) has several of his own too and they are really nice.

The two latest projects on the ECB side are the Motorola 6809 Host Processor board. I built a prototype and it is working fine. It runs a modified version of the Motorola "mini bug" software and a corresponding application on the N8VEM SBC to communicate with it. The 6809 operates in parallel with the Z80 based SBC as a "host processor" which appears as a peripheral to the SBC "bus controller". The 6809 host processor has limited IO but a memory map that's almost completely clear. It has 64K of RAM and 2K of ROM (actually, its Flash and reprogrammable in circuit). It is also designed with its own expansion bus in addition to the ECB interface so it can mount its own devices on a mezzanine bus in parallel with the regular N8VEM system.

My plan is/was to port FLEX or CUBIX to the system but I got distracted by the pretty lights again and my attention turned to other things. The summary is the PCB is almost complete in its trace routing and I am getting ready to make a manufacturing order for PCBs. If you are interested please let me know. The 6809 host processor is definitely an acquired taste, its rather different but I think it has tremendous potential.

You can see all the latest data and photos at the N8VEM wiki here:

The next major development is I've started working on a Video Display Unit (VDU) for the N8VEM system. There are already some nice things like Vince's
PockeTerm which allow the use of VGA monitors and PS/2 keyboards. That is a great system but the VDU is quite different. Its more like a true video card with the capabilities of what you'd get in a KayPro 10. Basically its a simple SY6545 system for character mode video. You can do limited graphics using characters similar to how this was done on CP/M systems of the era.

I've just started on this project so it will be a while before its done. I've got a basic design template and a schematic in work. Also the prototype is started. Not all the design features are set quite yet but I want to establish a working "core" before expanding on this feature set. You can see the latest including the picture of the prototype board in development here I would really like it if someone would like to follow along and build the prototype with me. I think it would be fun and highly educational. Also it would help to have separate eyes on this design as the video is notoriously tricky circuitry.

There is some work going on in the S-100 side but that's another thread. If anyone is interested in joining the N8VEM project please contact me or post here.

Thanks and have a nice day!

Andrew Lynch
 
Hi All! I've been working on the N8VEM VDU board. Tonight I got the board to generate some video so I posted some pictures on the wiki in the VDU folder. The project is not done yet although I think its over the hump. What's left is to write some better test software to exercise the board and then to add an 8255 for a PS/2 keyboard interface.

Thanks and have a nice day!

Andrew Lynch
 
The video looks great. Proper retro green screen too. That is on a TV as I gather vga is a bit too fast. The pocketerm uses TV and VGA. It has the potential to do colour as well as you can set pixels to any colour, though limited to slightly odd screen sizes on vga.

Andrew, will you be implementing VT100 codes and Wyse codes so we can run the games?

As for keyboard, the source code is on the wiki for driving a PS/2 keyboard via an 8255. Sing out when you get to the keyboard part...
 
The video looks great. Proper retro green screen too. That is on a TV as I gather vga is a bit too fast. The pocketerm uses TV and VGA. It has the potential to do colour as well as you can set pixels to any colour, though limited to slightly odd screen sizes on vga.

Andrew, will you be implementing VT100 codes and Wyse codes so we can run the games?

As for keyboard, the source code is on the wiki for driving a PS/2 keyboard via an 8255. Sing out when you get to the keyboard part...

Hi James! Thanks! The N8VEM VDU board uses a regular composite monitor (CVBS) rather than a VGA monitor. It is compatible with TV sets that accept composite signals. My goal is for a vintage like video board similar to a KayPro 10 or Vector Graphic FlashWriter II. It is simple monochrome character video just like you'd find on the early microcomputers.

At least in theory, the VDU could be bumped up to VGA speeds by replacing the dot clock (16 MHz) with a 25 MHz unit and some custom programming. Also it probably would require larger video RAM if I keep the character gen ROM the same. It currently uses 80x25 character video with each character being 8x10 dots (640x250).

The minimum VGA signal would be 640x400 which would require 40 vertical characters. I suppose a different character generator ROM with 16 dot tall characters would work to preserve 80x25. However the big problem is that VGA speeds require a much faster character clock. The current SY6545A allows for a 2MHz character clock but boosting to VGA speeds means at least 3 MHz. SY6845EB/UM6845EB chips support those speeds but its drifting away from what I really wanted to do and adds complexity to a really nice simple design.

As for software support, my plan is to build a simple application that demonstrates the features of the board. It will have a library of simple functions like clearing the screen, placing a character at a position, moving the cursor, etc. I am rather leaning away from CBIOS support or any advanced terminal emulation as I would like to "spin up" this PCB and move on to other projects. I think if N8VEM builders would like to extend the software functionality it would be fairly straight forward.

What I'd really like to do is add PS/2 keyboard, PS/2 mouse, and parallel printer support. However, I am not sure I can squeeze all those functions out of a simple 8255. I am doing some research on the subject.

Thanks and have a nice day!

Andrew Lynch
 
Hi All! The PCBs arrived for the N8VEM 6809 host processor board. I have several available if anyone would like to build one. Please contact me for arrangements. As usual, the PCBs are $20 each plus shipping.

If anyone is interested in a project to port FLEX, CUBIX, or OS-9 to the N8VEM 6809 host processor please let me know. The primary OS for the N8VEM home brew computing system is CP/M on the Z80 based SBC however this is not a mandate. Other operating systems such as FLEX or CUBIX should run. The 6809 host processor currently runs a modified version of the Motorola minibug monitor.

Thanks and have a nice day!

Andrew Lynch
 
Hi! I got the VDU prototype working and it seems to work well. The PCB is layed out and in the trace optimizer. It will probably be in there for quite a while as it is a complex circuit.

In the meantime, I am working with some other builders on the N8VEM project to make a "PropIO" board. It is an ECB board with a Propeller and various IO. Since the Z80 is able to communicate with the Propeller directly (no UART interface) via IO ports the transfer rate should be very quick. The current design supports VGA monitor, PS/2 keyboard, and a micro SD interface. The PropIO is built using standard off-the-shelf parts and a N8VEM ECB prototyping board. There are pictures on the N8VEM wiki in the DWM-PropIO folder.

The PropIO design is rather fluid right now. It is not using a lot of the PCB so I am considering adding a second Propeller and more IO to it. I'll keep you posted on how it goes. If you are interested in joining the prototyping efforts, please join us on the N8VEM mailing list and wiki.

Builders of all skill levels are always welcome in the N8VEM project. It is a fun project for brand new electronics hobbyists through highly experienced professionals. There is something for everyone and we are having a lot of fun!

Thanks and have a nice day!

Andrew Lynch
 
Hi! Just a quick update... One of the builders has taken on the project of making a FDC CBIOS for the Disk IO project. It seems at long last the dream of a N8VEM that can actually use real floppy disks may be finally coming true.

This would be a huge moment for the N8VEM project if it comes to pass. I certainly hope so and it is looking good at the moment. Keep your fingers crossed. There is a draft FDC CBIOS up on the wiki and a dramatically improve disk monitor in the works too.

The VDU board seems trapped in trace routing/optimizer purgatory. I am not sure when it will be done but hopefully while we are still young. The PCB trace routing exceeded some type of complexity threshold and the router has been having an awful time with it.

Thanks and have a nice day!

Andrew Lynch
 
Floppy disk access will be nifty. Posts are coming thick and fast on the forum as it comes together.

Andrew - the 30 boards I ordered arrived today and I'm going to keep a few and send most of them over from here in Australia to you in the US as it will mean shipping costs will be lower for most people. I soldered one up today and it booted 1st time. The design is getting very reliable now.

Also, some crazy experimental stuff going on with the Propeller. Take a 40 pin prop chip, eeprom, ram chip, max232 and a thumbnail sized sd card. Load up 8 disk images of 1-8mb each off the Altair SIMH project and fire up a Z80 emulation in software. It can do Mbasic, Wordstar and even games - all the stuff the N8VEM can. And today xmodem is working so can transfer files.

The Prop emulation is still experimental but shows great potential. Coupled with the wireless network we already have working, the prop emulation could act as a file server for a N8VEM network.

I have to stop posting now - my soldering iron is cooling down!
 
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