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Powertran Cortex

danwerner21 said:
I posted this in another thread as well, but adding it here for a bit more visibility . . .

I am working on another clone of Stuart's MiniCortex board. This is in an ATX format -- I have also added a sound chip, keyboard interface and expansion ports. I am still reviewing the design but hope to order boards for testing in the next week or so. Would love any feedback/comments!

CortexPC ATX

I do not expect this to be the final version of the board, as I think that eventually the keyboard interface needs to be further built out, the bus interface is totally unproven and I may want to add a bit more hardware to the board as there is a ton of open space. ( floppy disk interface, centronics parallel, and perhaps a CH376 USB . . . )

I will be posting updates to the github repo linked above and will be filling out the documentation more as testing proceeds.

Dan Werner
vic2020dan - at - gmail.com
Click to expand...
The minicortex clone(ish) is working well. MDEX, Cortex basic and Unix all working and both sound chips and the nano 9918 work. I need to put this in an ATX case, and I would also like to put a bit more work into the firmware, but it is working quite well. I need to update some of the information in the readme file, but everything in repo should be current and usable. https://github.com/danwerner21/CortexPC1000005759.jpg
 
danwerner21 said:
The minicortex clone(ish) is working well. MDEX, Cortex basic and Unix all working and both sound chips and the nano 9918 work. I need to put this in an ATX case, and I would also like to put a bit more work into the firmware, but it is working quite well. I need to update some of the information in the readme file, but everything in repo should be current and usable. https://github.com/danwerner21/CortexPC
Click to expand...


MiniCortex Board mounted in an ATX case:
fivea.jpg
 
So gradually making progress…..I now have it booting up reliably.

At first it was very flaky, which eventually I traced to dodgy sockets….been gradually changing them for turned pin type and done about half of them before it became reliable.

Work done to date….
Changed sockets for all the ram, cpu,dma, most of the glue logic chips around the 4500.
New ram chips
Tried a 9918 to get a better video with some success. But a pico99 has cured all the video issues and avoids the extra external cvbs to vga conversion.
New power supply ( switched mode )
Fitted mapper chip and ebus components

Blew a few chips by stupidly reversing one end of the keyboard connecting cable….

At the moment trying to get the wd2797 floppy controller to work - I have my original floppy pcb home made board from around 1990 which was working when I crated it all into storage but at the moment I have my doubts about it.

At first I could type boot and it would lock up suggesting it was waiting on the drive but all I get now is hardware not found…..so going to get a spare 2797 from eBay and try that. I suppose I can check if the 2797 registers are visible via MON….. just need to find more time.
 
So gradually making progress…..I now have it booting up reliably.

At first it was very flaky, which eventually I traced to dodgy sockets….been gradually changing them for turned pin type and done about half of them before it became reliable.

Work done to date….
Changed sockets for all the ram, cpu,dma, most of the glue logic chips around the 4500.
New ram chips
Tried a 9918 to get a better video with some success. But a pico99 has cured all the video issues and avoids the extra external cvbs to vga conversion.
New power supply ( switched mode )
Fitted mapper chip and ebus components

Blew a few chips by stupidly reversing one end of the keyboard connecting cable….

At the moment trying to get the wd2797 floppy controller to work - I have my original floppy pcb home made board from around 1990 which was working when I crated it all into storage but at the moment I have my doubts about it.

At first I could type boot and it would lock up suggesting it was waiting on the drive but all I get now is hardware not found…..so going to get a spare 2797 from eBay and try that. I suppose I can check if the 2797 registers are visible via MON….. just need to find more time.
Click to expand...
Looks like we're running in parallel! :) Have look here A Powertran Cortex is (re)Born
I had some good fun getting the Disks working but it turned out to be a naff socket. Now it all works dead reliably. I've even installed a GoTek drive.
 
IMG_0210.jpeg
So it’s all on the workbench….. reliably booting from the ROM but still struggling to get the disk drive working, found some small issues and a duff wire link on the floppy pub but still not managed to read cdos2.0 from my disk ( starting to suspect the disk drive. / disk is duff )

The pico 99 replacement for the VDP is fantastic….. well worth it !

Disk wise, if i manually run the floppy head out then when typing boot the drive seeks but as soon as it hits track 00 I get the hardware error

If I leave it on T00 then the error is instant - not enough disk rotation for it to be reading the checksum so not sure at the moment why it’s erroring.

Going to eBay some more TTL chips as I need some spares to swap out just in case it’s a chip error.

I am also going to get a greaseweasle to test the drives and the disks then maybe also a Gotek floppy replacement. But got to get rid of the “hardware not found” for the disks first.

Anyone else got the 2797 controller or are you all 9909’s.

You can also see my ROM extension board that lets me use 2764 instead of 2564 …. Once I get it working I intend to rework this and the 2001 replacement headers into some new boards to allow maybe larger roms, static ram and a new floppy sub board.
 
Good going!! I had some issues getting the disks working, it turned out to be naff sockets which I found by tracing all the control signals back from the disk to the 9909 controller. It took a lot of "BOOT" cycles and restarting the Cortex but it paid off in the end. I also had some excellent help from @Stuart . I don't have greaseweasle but @plagued has done some extensive testing on his Cortex drives with it. He may be able to help.
Keep up the good work! :)
 
Yahoo……played with a greaseweasle and checked out the drives, the best one is double sided 80 track 5.25 and after finding a broken track on the controller board and adding a few extra decoupling caps it seems to be reliable.

Still not fully finished as the first time I ask it to boot the disk it fails then the second time it boots so maybe something not quite right

But great to see CDOS again after about 30 years…..

IMG_0233.jpeg
 
Hurrayyy! That's magic news!!! I see you are using the 2797 Controller. Sorry I can't help you with that specifically as I have the TMX9909, but you can't be far off. Keep at it.
 
image.jpg
So here we are…… all in the box and out of the workshop and on my desk
So it has the 2797 disk controller, pico9918 display controller and. 4 floppy drives. Not got the gotek loaded just yet but working on it.

It’s still got an odd thing in that every time I start it up and hit boot for the floppy’s it stalls for 5 seconds, runs the disk and reports hardware not found…..then when I type boot again it loads and boots the DOS.

Going to redo the floppy controller board with a new PCB as the one in it I made about 38 years ago and I do suspect it may not be great……just depends how long it takes to get the boards made for me.
 
That looks great!! Very polished. It fits in well with the edition of "Practical Computing" on the desk. Or did you take this photo in August 1980 and only just post it? Of course not; the Cortex didn't come out until 1983. :biggrin:
 
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