Thanks everyone for the interest. I don't have a blog yet. But I really should start one. I really like the format that BMOW does with his projects. I might follow something similar.
I'll either post my progress here (if no one objects) or just post a link to my eventual blog.
In the meantime, I gathered up parts that I already have on-hand. My dream is to design a "Mac like" computer that would fit between the Mac 512K and Amiga 500. Closer to the Mac because the Amiga had advanced chips for it's day and I'm a HDL newbie.
I will be wire-wrapping my first prototype starting this weekend. The CPU of choice is a 68SEC000. I have bought a TQFP-64 to DIP converter so I got some soldering to do. The final design will likely use a "largish" FPGA and maybe some smaller CPLD's. I don't want to go insane on the FPGA choice. Mainly because my eyesight restricts me to soldering TQFP-100 to MAYBE -144 packages. I have no interest in BGA.
So, what do I actually have right now?
Almost everything. However, they are a mixture of small boards, slower parts, etc. So not the final specs. For example, I will be using two SRAM chips for 16 bit memory that run 55ns. BUT, my final design will incorporate 16-bit SRAM at 8-10ns with 1 MiB minimum. I thought about getting DRAM chips because they are very cheap and 16 MiB would cost almost nothing. But, I don't want the extra hassle of DRAM refreshes and column/row logic. Plus, no affordable computer in 1984 - 1986 had 16 MiB anyway. 1-2 MiB for my final design sounds good and the 16-bit SRAM chips are not that expensive.
On my CPU adapter, I have a small bag of wire-wrap pins that I will have to painstakingly solder one by one so that the adapter board can be used with wire wrap. Not to mention the small SMD CPU itself.
Anyway, my parts so far are (for prototype):
68SEC000 CPU (with adapter)
512 KiB SRAM 55ns x 2 (used for odd/even) memory. 1 MiB total RAM.
128 KiB ROM 70ns NOR flash x 2 (used for odd/even) memory. 256 KiB total ROM.
DUART Serial (2 ports) via NXP 28L92.
ATF1504 CPLD (32 I/O)
ATF1508 CPLD (64 I/O) - 7.5ns
TinyFPGA A2 (~21 I/O)
TingyFPGA BX (~41 I/O)
Parallax Propeller MCU (8 cores, 32 I/O). Possibly used for audio (has great SID emulation) and/or general I/O for keyboard/mouse, SD, etc.
Eventual specs for final design:
1-2 MiB RAM
256 KiB ROM
SD card running FAT16
USB mouse/KB (MAYBE PS/2 if USB proves to be a headache).
640 x 480 VGA.
I don't want SVGA, massive sprites, etc. I'm leaning more towards a simple frame buffer with possibly hardware blitter.
For colors, I'd like to shoot for at least 256 (8-bit).
I'm undecided if I want to force a static display (like the original Macs) or allow a more dynamic display like the Amiga (and later Macs).
Sound. (duh..lol). SID emulation sounds good...but I probably won't use it. If you have memory, then audio buffers and DAC's sound so much better. Just compare the Amiga against the C64. The IIgs should be noted because of the massive number of channels...but still, sampled audio will probably be the way to go.
Right now, most things are up in the air.
More than likely, I will use the ATF1508 CPLD as a simple VGA controller and MMU. Mainly because it has the most pins. But I'm sure I will find something to do with those other PLD devices.
If/When I finish my final design, I hope to have a smallish 4 layer board made. Which I will make available.
If this is successful...if I love working on it after all of that....and people still want it....I might look into a second revision where the 68K is handled within an FPGA. Not true "retro", but much easier to sell and source.
Any questions, just ask...
Wish me luck!!
PS, I still haven't thought of a name yet. I want something catchy but not cheesy. One thing I like about "Macintosh" is that it sounds good...looks good...and can be shortened to "Mac". Plus, it falls inline with "Apple". It would be hard to beat that. :-D
