I just took delivery of my new Zilog Z180 with NEC uPD7220 Graphic Display Controller (GDC) dev board. Will start building this weekend. The purpose of the board is to demonstrate the uPD7220 Graphics Display Controller in a stand-alone all-in-one SBC.
Board contains Z180 CPU, 512KB Flash ROM, 1024KB SRAM, RTC, two serial ports (TTL & RS-232), PPIDE (CF-IDE), PS/2 Keyboard & Mouse ports, and uPD7220 GDC with BT478 RAMDAC. Intended to use VGA frequency monitors and standard PS/2 keyboard & mouse. Uses RomWBW as it’s operating system.
Of the five PCBs, four are claimed so I still have a spare if someone is interested in building their own. However, this is a prototype board and likely will have changes before next version. Purpose of prototype is to ensure the design works as intended and make any necessary corrections.
For those wondering what is a uPD7220, here is an article explaining
I have started early build and test focusing on passives for now like resistors and capacitors while verifying the power nets are working. Seems to be OK so far but keeping notes for improvements in the V2 version
I have not heard of anyone building their own Z180GDC using the Gerbers on the Github repo but I suppose it is possible. If you are doing that please monitor the prototype page for build and test notes as I go through my own build. This will save you some of the problems and annoyances I am discovering and will make your build easier and more successful. This is where the prototype build and test notes are captured: rhyophyre/Prototype at main · lynchaj/rhyophyre (github.com)
PS, if you are building your own please don’t be shy. I’d really appreciate knowing how it is going for you and what you discover, like and/or dislike
Good news on rhyophyre; team got first boot using a modified N8 RomWBW configuration! We’ve just started but major progress – CPU core only at this point; minimal IO. Need some time for things to settle out and let the team work out some details but major milestone achieved! Thank you to the build and test team! You are incredible!
Making more great progress today. The DS1210s work for NVRAM as does the RTC for keeping track of time and various utility functions. PPIDE is working and it looks like the PS/2 keyboard and mouse interface is working. Still a lot to do but the big show is coming up to get the uPD7220 GDC section working.
Build and test continues on the rhyophyre prototype board. Making good progress and so far all the major subsystems check out although there have been a few discoveries. I am documenting the fixes in the repo prototype build construction notes so be sure to check those out before starting your own build. Some changes will be reserved for the Z180GDC V2 board which will be discussed later.
The final stage of check out is the uPD7220 subsystem itself. There is a test program which initializes the uPD7220 and successfully generates an empty VGA screen. The good news is the VGA monitor recognizes the display and locks on it. However, this is only a partial initialization useful as a demonstration it can generate a VGA display. Still to go is initializing the RAMDAC and actually programming the uPD7220 to display useful information. Great sign to get the VGA monitor to sync to a display signal though.
Making progress on Z180GDC V1, adding a few items to builders notes on the repo but overall going well. All subsystems check out either fully or mostly. Now working on uPD7220 to produce VGA compatible video. Getting very close. Have two test programs and between them we can create an image with one program (but no sync) and use the other to get the monitor to sync to display the image. Very close but programming the uPD7220 can be rather tricky so it may take a while.
Yes, for a first generation prototype it is holding up amazingly well. Usually, my prototypes by this stage are a mass of flying leads, dead bugs, cuts, jumpers and all sorts of modifications.
There are 6-8 patch wires on the copper side of the board but no showstoppers. Mostly annoyances that we easily fixed. Overall, I am very happy with how it is turning out.
Looking forward to the uPD7220 test code to ring out that subsystem. The goal being this computer will be self-contained and not need a PC for support eventually. Connect to VGA monitor and PS/2 keyboard & mouse for console.
Have a lot of plans for Z180GDC V2 which will be a modest expansion on this concept.
Initial build and test of Z180GDC V1 is making solid progress and has advanced to the uPD7220 video section. There are two test programs written by members of the team which now present a video image to the monitor. This is a significant milestone event!
Sorry about the terrible image quality. It looks much better in person and the monitor is less dusty than it looks in the photo. It doesn’t do it justice but it gives a solid idea of what’s being displayed. It is 16 colors at [email protected] Hz refresh for basic VGA
Z180GDC V1 project seems to be coming along nicely. Hardware seems to be working fine although there seems to be some mysterious blanking during drawing operations on some LCD monitors. Some work fine and other have random blanking. Looking into what is causing this phenomenon.
The team has written some demonstration programs which work well including a text terminal demonstration. All things considered I think it works remarkably well and smooth. So that’s good news.
Would like to have more people build this board and try it out to shake out any other bugs and/or write
software programs. All of the tech data can be found here including PCB Gerber files
It looks like we found the root cause and a fix to prevent the random blanking on some LCD monitors. It has to due with DRAM refresh during drawing operation video memory writes. Disabling the DRAM refresh fixes the problem with a simple patch. Since the design uses SRAMs and no refresh is needed at all. Not an obvious connection but glad to see it is finally resolved.