My eZ80 system project

[Chris B]

A project I worked on heavily about 10 years ago during a bout with unemployment has come back to life and is progressing.

I designed and built an application board for the Zilog eZ80 development kit. It adds the following:

4 Zilog SCC serial ports. So now the eZ80 kit has 6 serial ports.

A Compact Flash interface. Currently implemented as 16 64 mByte drives A: thru P:

A 6-digit address display that provides great visual feedback on what the eZ80 is doing.

I have MP/M working on it. I'm able to run some programs. Right now I'm trying to get Zmodem working. It's a fantastic solution for moving files in and out of any CP/M system. On my Mac, I run a Mac-version Zmodem. I can move directories back and forth in minutes.

The MP/M I have running is functionally the same as the DRI original. I took a dis-assembled version that Bruce Jones did in the 1980s and extended it so that it fully supports both original Z80 code and 24-bit eZ80 code, simultaneously and automatically. Of course, the re-written OS takes full advantage of the many new and powerful instructions unique to the eZ80, so it runs incredibly fast. An eZ80 clocking at 50 mHz is the equivalent of the original Z80 running at about 200 mHz overall. There are a couple of instructions which are the equivalent of a Z80 running at 800 mHz.

The Zilog eZ80 development system enables debugging support we could only dream about in the 1980s. Single-stepping and breakpoints right in the source code, for instance.

So why am I doing this? First and foremost, it's incredibly fun and fascinating. I most enjoy working on computers in which ALL of the code is accessible (and since so much of it is written by me, it elicits a lot of pride when it is running and stable). 50 million machine cyles per second.

The ability to run and play with the large legacy of CP/M software programs is part of the allure.

And there is a real practical use as an OS for me. This system is capable of interfacing with many modern devices that have RS-232 interfaces. Some on my list to support later:

X-10 for controlling my lights and swimming pool pump.
My solar inverter and solar charge controller both have RS-232 interfaces. I intend to extract performance data live and send it to an RS-232 LCD panel in my kitchen.

The application board that I built is built with wire-wrap. I eventually will make a version 2.0 using my PCB Cad.

If anyone is interested, I can share the schematic, photos and code.

I have most of the MP/M code running in 24-bit mode and so the Common Bank starts at E000, just 4K of RAM, compared to DRI MP/M needing 16K of RAM. Most of my code is running in 24-bit ADL mode.

I do have a long list of to-do's that might be of interest to others to participate.

A cool utility would be a replacement for ZSID that supports access to the full 16 megabyte address range as well as decoding the extended instruction set. It will be a while before I get to it so if someone wants to join in ....

I'm adding a "Set OS Mode" system call so that to an application can see this system as either an MP/M system or CP/M Plus system.

Is it possible to post photos on this thread?

Chris Brock

[Steve Nickolas]

On Sat, 8 Feb 2020, Chris B wrote:

> Is it possible to post photos on this thread?

You could probably upload and link to a site like Imgur.

-uso.

[Tony Nicholson]

Sounds interesting Chris.

I started a thread about a year ago on the RetroBrew Computers Forum regarding the eZ80. You might like to take a look at

https://www.retrobrewcomputers.org/forum/index.php?t=msg&th=354&start=0&

and perhaps join the discussion there as well.

Also, if you're a GitHub or SourceForge (or similar code-sharing site) user, you could consider making your source-code, photos and schematics available there (for posterity!).

Tony

[norwe...@gmail.com]

On Saturday, February 8, 2020 at 4:55:21 PM UTC-8, Chris B wrote:
....<snip>....

> If anyone is interested, I can share the schematic, photos and code.

I'd definitely be interested, Chris. I have a eZ80F910200ZCO development kit, but I was never able to get it working via the network interface provided or the ZPAKII (and software) that came with it. It includes the "E-NET Module" and the "evaluation platform". Love to see what you've done with your eZ80!!

Roger

[Chris B]

I see that although one can't post photos the group threads, I am able to use the "reply privately to the author" feature to send photos to anyone that asks me to reply. I just sent photos to Roger (separately).

[Lamar Owen]

Yes, Chris, come on over to Retrobrew computers.org..... it may take a bit of time to get registered, but you'll be very welcome.

[AB]

Sounds very interesting! I've been looking for an MP/M implementation that has serial capabilities for some while now.

cheers
andy

[Steven Hirsch]

On 2/28/20 9:47 AM, AB wrote:

> Sounds very interesting! I've been looking for an MP/M implementation that
> has serial capabilities for some while now.

I'm not motivated enough to wirewrap anything of that complexity. Any chance
of doing a PCB layout?

[Lamar Owen]

There are several in the Retrobrew computers.org group who could easily do that board, if they will. Otherwise I might try my hand at it. I don't remember if that package I got had a schematic or not..... Time to break out kicad.

[Chris B]

On Friday, February 28, 2020 at 3:01:49 PM UTC-8, Lamar Owen wrote:
> There are several in the Retrobrew computers.org group who could easily do that board, if they will. Otherwise I might try my hand at it. I don't remember if that package I got had a schematic or not..... Time to break out kicad.

===================

I drafted the schematic in McCad.I haven't put much thought into making a PCB because my preference is to evolve this project to the next step. E.g, I want to switch from Compact Flash to SD Card. There are several eZ80 development kits available, however, the version that my project uses as its host was discontinued fairly recently. Instead, I want to switch to the mini-E-Net module which can be purchased from Digi-Key or $65.

However, since the timeline for that is unknown, anyone that wants to build a duplicate of what I built ... I'm happy to support and answer questions.

I joined retrobrew.org, so thanks for the invitation.

Now for a general discussion of what the eZ80 is and its place in the Z80 progression of CPU designs.

In the early to mid-1980s, Zilog was one of the biggest microprocessor vendors, if not the biggest in sales volume. Its installed base of customers eagerly anticipated the Z80's follow-on. Year after year, nothing happened other than rumors of a Z800. The Z8000 cam ot but wasn't object code compatible with the Z80. A Zilog employee told me in the late 1980s that Zilog couldn't stop designing the Z800 and put it into production. He said that periodically, a Zilog engineer would read a technical article about some advancement in CPU architecture and Zilog would push the ship date out and go back and design in some cool new architectural feature. Eventually the clock ran out and the industry focused on Intel's evolution of microprocessors.

In the early 1980s, Hitachi licensed the Z80 and designed the HD64180, the first practical evolution of Z80 architecture. Zilog later brought that design into its product line as the Z180. The Z800 evolved into the Z280. Wikipedia describes it as a "failed product". Production ceased a long time ago, however, there were customers using it. Hayes shipped tens of thousands of Z280s in many of their modem products in the 1990s. Not exactly my definition of a failed product. On the other hand, the Z180 preceded it and it's still available.
The Z380 built on the Z280, however, it was scaled up in ways that didn't matter for what Z80s are most often used for: micro controllers.

The eZ80 built on all previous Zilog Z80 follow-on products, and since it was designed in the late 1990s, it utilized design advancements not available earlier. First is pin count. The Z280 conserved pin count and was difficult to design with because it had a multiplexed address/data bus. The eZ80 is actually easier to design with than the original Z80. The eZ80 is optimized for fast (and inexpensive) static RAM. It uses faster silicon, 50 Mhz. The standard cell tools allowed the designers to throw in lots and lots of cool things without having to design from scratch. Ethernet MAC, I2C, SPI, PLL, PWM, UARTs, RTC, CTC, GPIO, IrDA, flash RAM, internal RAM. And because it came after all other Z80 follow-on products, it provides the most seamless way to support pure Z80 code, while adding 24 bit addressing and register math and significant extensions of the basic Z80 instruction set. The LD instruction is an example. When using pointers, a Z80 can only move 8 bits at a time. The eZ80 can do 8, 16 and 24 bit moves with pointers. My view is that the architecture is genius. In writing s/w, you can switch back and forth between Z80 and eZ80 mode on a per-instruction basis. Z80 code can call an eZ80 subroutine and visa-versa. The eZ80 is far and away the best documented Zilog Z80-compatible CPU. The hardware manual is 370 pages and the programming manual is 402 pages. The eZ80 is still in production; all others besides the Z80 and Z180 are no longer made.

[Chris B]

I belong to a local model railroad club, and since California is in a mandatory shelter-in-place right now, our club no longer meets weekly. But we do meet; we meet by using Zoom conferencing. Within this topic thread about the eZ80, I've received emails from about a half dozen persons expressing interest finding out more about eZ80 matters. I was thinking it might be fun to do an informal eZ80 virtual workshop by Zoom conferencing. I could show more detail about my project, hear about other's similar projects. We could share details/tips on using ZDSII developments. Specific source-code walk-throughs are possible if there is interest.