| Z180 upd7220 GDC SBC [message #9724] |
Thu, 03 February 2022 04:17  |
lynchaj
Messages: 1080
Registered: June 2016
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Senior Member |
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Hi
I am interested in pursuing a Z180 upd7220 GDC SBC project and have an initial design. It is not done yet, but the attached files should give you a pretty good idea of where this is headed. I anticipate only cosmetic improvements between now and PCB build and test.
It would have a Z80S180 CPU with two serial ports, 512KB Flash ROM, 1MB SRAM, RTC, PPIDE, and PS/2 keyboard and mouse controller plus a NEC upd7220 GDC graphics controller. It should be capable of 640x480 by 16 color graphics with a 25 MHz dot-clock. The ECB upd7220 GDC was capable of 800x600 by 16 colors with a dot-clock upgrade to 40 MHz. I think this design would as well but would like to keep that as a goal rather than a requirement.
My desire is to gauge what sort of interest, if any, exists here. I would like to order some PCBs from JLCPCB and will ship those inside the US. People outside the US will have to order their own using the Gerber files once they are available. This is a large PCB (8.5"x11") with a lot of components so it would be a sizable investment plus time and effort.
If there is interest here that would be great but if not, I'll probably just keep the project private. Please let me know if you are interested in building one of these boards. Either post in this thread or contact me by PM or email if you have my address already.
Thanks, Andrew Lynch
[Updated on: Fri, 18 February 2022 08:51] Report message to a moderator |
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| Re: Z180 upd7220 GDC SBC [message #9735 is a reply to message #9734] |
Fri, 04 February 2022 06:07  |
lynchaj
Messages: 1080
Registered: June 2016
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Senior Member |
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mscane wrote on Fri, 04 February 2022 07:34Hi Andrew,
That looks like an interesting project.
A couple of thought come to mind:
1. Power consumption. I recall the original 7220 board consumed a fair amount of power, I doubt the linear regulator would handle the load or would get pretty hot. Would it be better to incorporate a switching regulator or just make the board 5V only?
Hi Max, Thanks! Yes, I am concerned about power consumption on both the Z180 and upd7220 sides. Both use a lot of current. I added a 5V DC regulated direct connector and sized the VCC & GND traces for 3 amp draw. I estimate it should be less than 3A but want some margin. The 9V DC unregulated barrel jack has its traces sized for 6 amps draw although I really hope it doesn't come to that.
There is also a 5V regulator (LM7805K) in the TO-3 package which is able to source up to 3A of current in a regular package. With a ground fill zone as a thermal radiator it should be able to produce enough current for the board.
Many of the components on the Z180 are available in CMOS versions although on the upd7220 side it is all 74LS and 74F for speed requirements. Possibly there could be some 74HCT substitutions in a few areas but not a lot. I am looking for CMOS versions of the 32KB cache SRAMs which would save some as well.
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2. PPIDE. 82C55s are getting harder to get these days and using it does slow down data transfers due to the need to bit bang signals. Most likely you would be using a compact flash card which could easily be connected directly to the data bus (eg Mark IV) without needing the 82C55.
Thanks, I will look into this.
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3. SD card. Compact Flash cards are also getting scarce. Would it be possible to add an SD card (similar to N8)?
The N8 had an SD card but as I recall it was connected to the Z180 ASCI port which turned out to be a bad idea. The serial port sent the bits in the wrong order to what the SD card format was expecting and so all the data had to be manually reversed in order to get it to work. Apparently, it was dreadfully slow and was unpopular. At least that's what I remember although things may have changed. I think these days to use SD you would have to have some kind of MCU or parallel to serial interface (not a UART) to get acceptable performance.
My goal is 100% RomWBW compliance and I know the PPIDE with CF-IDE adapter works out-of-the-box. It has worked great on the Z80 MBC project and really advanced it much further than I could have all on my own. RomWBW is a breakthrough technology which makes these projects much more achievable. So much that I am designing the project to achieve maximum RomWBW compability.
At one point, RomWBW supported upd7220 and there are still traces of it left in the source code although I think it has been mostly deprecated in recent versions. My plan is to implement a graphics character pseudo-character mode with the upd7220 so it acts like a text console at least at first. Then later implement the more graphical functions like possibly GSX-80 or something similar. Character mode is critical for RomWBW compliance though, so it has to be top priority.
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4. Board size. Given you are approaching Micro ATX size (9.6 x 9.6), would it be worth while making it capable of using an PC case/power supply
I'm considering that for a subsequent version. I have some ATX PCB layouts but this board is intended to be a prototype for the work bench. Almost certainly there will be a bunch of changes which will require a respin and we can address reformatting the PCB layout then. I am hoping the debug features (spare sockets & prototyping area) can be removed and shrink down the board somewhat.
The other alternative is to use the JLCPCB 3D printing service to make a custom case for it. Dan Werner did this for his WE816 SBC and it turned out great. I can see something akin to that for a large flat PCB like this one.
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Cheers!
Max?
Great feedback, let me consider your ideas. Thanks, Andrew Lynch
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| Re: Z180 upd7220 GDC SBC [message #9736 is a reply to message #9735] |
Fri, 04 February 2022 08:41 |
lynchaj
Messages: 1080
Registered: June 2016
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Senior Member |
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Hi Max,
I went back and re-read the 7805K datasheet and I must have mis-read it. It can't handle 3A current so I am going to remove it and just use the 5V DC connector from a power supply.
Good catch! Thanks, Andrew Lynch
PS, correction, there are 7805s that can handle 3A but they are mostly TO-220 packages, so I switched over to the TO-220 footprint with a lot of room left for a large heat sink. That should help dissipate the heat. Specifically, it is the MC78T05. I must have gotten my wires crossed somewhere
[Updated on: Fri, 04 February 2022 13:05] Report message to a moderator |
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| Re: Z180 upd7220 GDC SBC [message #9760 is a reply to message #9738] |
Mon, 14 February 2022 04:13 |
lynchaj
Messages: 1080
Registered: June 2016
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Senior Member |
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Hi
A quick update on this project; I have the PCB in FreeRouting optimizing. It's been there for over a week and will likely be there a while longer. It is a big and complicated board so it takes a long time to get a decent autoroute completed. FreeRouting can only do so much so some work has to be done by hand.
When it completes or is at least close enough I will order some PCBs from JLCPCB. Normally I get 5 PCBs per order. I will use one for certain and probably 2 or 3 to others. I think there might be a spare board left over so if you're interested in building please let me know. I can order more PCBs but I doubt that many people are willing to build the prototype.
Thanks, Andrew Lynch
PS, I have been slowly ordering parts for my build and gathering up the stuff I have already on hand. It's a lot of parts although I have a lot from previous projects. The initial build will use a Z80180 I've had for a long time with a 7.3728 MHz clock. I have a upd7220 chip from before and am going to order a BT478 RAMDAC. Along with the 82C55 and VT82C42 those are the big ICs and the rest are mainly glue logic and memory.
[Updated on: Fri, 18 February 2022 03:44] Report message to a moderator |
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