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 Billy I: The 68K computer 
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Joined: Tue Dec 31, 2013 2:01 am
Posts: 76
Take good care of yourself, young man. We'll be here when you get back.

Mike B.

Sat Dec 05, 2015 6:52 am
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Joined: Thu Oct 08, 2015 11:57 pm
Posts: 55
Hello everyone! I have made a full, yet slow recovery, and now I'm back to finish this project! During my resting period, a friend of mine gave me an old Pentium 4 PC that I can scrap for parts. I found a nice 250GB hard drive, a CD drive, and a 400W power supply, which all went in Billy. I also found him a nice case, now he's starting to look more like a computer. Now all I need to do is buy some RAM slots and some RAM and finish this darn motherboard. Let's just hope this action by Intel doesn't screw things over for me: ... 30830.html

I'll get some pics of what I have so far tomorrow.

Sun Jan 03, 2016 7:56 am
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Joined: Thu Oct 08, 2015 11:57 pm
Posts: 55
Here is Billy in his flashy not so new case:
0103161147-00.jpg [ 211.85 KiB | Viewed 408 times ]

I had to replace one of the fans on the power supply because the intake fan's bearings were shot. The rest of the power supply, despite it's old age, still runs perfectly. I know 400 watts is a bit overkill, but at least I don't have to worry about running out of power when I start making add-on cards.

Sun Jan 03, 2016 8:36 pm
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Joined: Thu Oct 08, 2015 11:57 pm
Posts: 55
Well, things have gone downhill with this project. I got enough of the motherboard finished for the CPU to make NOP cycles, but when I plugged the board in, nothing happened. Then I realized that I tied DTACK high instead of low, so I fixed that. Well, instead of fixing the issue, the CPU still did nothing, but got very hot in the process, and the power draw went way up. It probably has to do with how messy the board was. So you know what? I'm scrapping the board and I'm just going to have a PCB fabricated. And while I'm at it, I'm going to redesign the entire system, from square one. So here's the list of features I want this thing to have that the original design didn't:

A more active northbridge, in charge of controlling the data flow rather than using discrete ICs
Same 32 pin DRAM setup as before, but this time with 16KB of backup SRAM
Variable DRAM timings (more control over RAM latency, which means support for devices with a broader speed range). The original design only supported 70 NS RAM.
Seperate chip for video generation
2 programmable timers
Interrupt support
Bus arbitration support
4 Expansion ports rather than 2
ATX standard power connectors (the original had god knows what kind of connectors)
mini ITX form factor (had no idea what form factor I was going for in the first place)
support for a CPU fan, in case this heating thing is supposed to happen
Support for both CPU packages, both PGA and DIP
Variable CPU clock(?)
RTC (for some reason I always forget this in my designs. But not this time!)
Improved power system

And that's my plan. But after a huge let down like that, I'm just going to take a break from Billy and make something using an ARM chip instead, since I'm rather good with SOCs and microcontrollers. That project will be up soon.

Tue Feb 09, 2016 2:48 am
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Joined: Thu Oct 08, 2015 11:57 pm
Posts: 55
I'm not dead!

So almost two years later, I find the box for this project and then looked at this forum post and decided to revive this old project. I have tons more experience now since I'm working on a Z80 computer and am also finishing up a Z180 game console. Since I've done two Z80 related systems, I want to step things up a bit and tackle this 68K that didn't want to work for me!

Looking back, I have found that I'm REALLY inconsistent with my designing! So for this project I'm making a list of things I want this computer to do, and I'm sticking to it.

- four expansion slots (three parallel and 1 serial)
- HDD port
- SPI BIOS with diagnostic utilities
- PS2 Ports for mouse and keyboard
- Serial port
- Overclocking and overvolting
- temperature monitor and fan controller
- Support for up to 12MB of DRAM, 2 slots, 6MB per slot
- External cache using SRAM, up to 128KB
- FPGA as northbridge with Cache controller, DRAM controller, and IO
- Built in ethernet, audio, and USB controller
- mini-ITX board layout

Mon Mar 06, 2017 2:28 am

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 573
Welcome back!

Mon Mar 06, 2017 7:37 am
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Joined: Thu Oct 08, 2015 11:57 pm
Posts: 55
BigEd wrote:
Welcome back!

Hahaha Thanks! It's been too long!

Mon Mar 06, 2017 7:41 am
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