68000 computer, including PIC RAM bootloader

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68000 computer, including PIC RAM bootloader

Postby takao21203 » Mon May 28, 2012 1:54 pm

I am working at this for a number of years, starting in 2005 actually researching the SEGA master system.
Originally I wanted to devleope a 68K cartridge for this console.

However it turned out that no official documentation is available, and SEGA does not seem to care at all about their 1980s technology. Back then for kids the cartridges were quite expensive! If they ever come accross my various web posting about this, they really should know how I feel about this.

However.

This changed into an independent project. At one point of time I was thinking about a television interface, using a graphics controller, made of memory, a PIC18F, and some logic chips. No CPLD or FPGA. But the prototype board back then was way over my head to complete. I did not knew how to use SMD back then, how to solder it to PCB. Adding wires to SOIC manually takes long hours...So this was not completed.

I made 5 or 6 68000 prototypes altogether in the meanwhile.

What I have in working condition is a RAM bootloader based on PIC16F884, 128K RAM, fully works! To do away with the EPROMs.

The best prototype so far:

108228645.v1336535532.jpg
108228645.v1336535532.jpg (79.54 KiB) Viewed 3850 times


However no schematics exist for that.

Currently two circuits are still considered to produce a working prototype:

1. factory made PCB, having on onboard 18F PIC, 32K SRAM, and a small CPLD.
68SEC000, 3.3v/15mA. This PCB can be very small! Most SMD parts must be created manually for layout.
And I lost the design file I already made when I reinstalled Windows some weeks ago.

2. PCI backplane using regular 5v 68000. i will most likely use a PLCC 68000 + plug-in board for this.
Here the PCI PCBs that go into the PCI backplane:

!BhHr60gB2k~$(KGrHqUH-D0EsMDIikbrBLHvl,uw!g~~_3.JPG


These should be here in the next few days.

What I consider altogether for visual output now is:

-television interface, composite video, and simple graphics controller (no color).
-1.8" TFT or 320x200 color LCD, have samples here for these, made proto board for 1.8" TFT but no wires added yet
-LED matrix?

Also I have some PIC32 here but never used one for circuit. I only recently changed from assembler to C language, MPLAB X now...maybe 3 or 4 months ago.

Do you have any comments or ideas for this project?

Eventually the PIC32 is already more powerful than 68000, but of course does not have interface for 16 MByte RAM, and is not comfortable for assembler, or it is not used much at all.

68SEC000 is still interesting these days, small SMD chip, and only needs 15mA. But RAM chips need a lot of power, actually. Eventually I want to emulate this using a PIC32, and serial RAM ICs. To reduce power consumption. But a lot of work I think.

I want to get a prototype working this year, and most likely this will be based on PCI backplane, and 18F PIC/5 volts.

The prototypes I made all don't have schematics, and this makes it hard to continue work on them, as I use different types of RAM chips, latches etc.

PCI backplane is good for this to carry all the address/data bus lines, not based on wires anymore! So leaving the old prototypes alone and build yet one more new one will take less time than to try understanding the previous ones (that I made myself but did not draw schematics).
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Re: 68000 computer, including PIC RAM bootloader

Postby sich » Fri Jun 01, 2012 1:40 pm

Haha...that's why we were taught to plan and draw schematic before getting our hands dirty with the actual circuit. Anyway, I'm just like you most of the time :P

takao21203 WROTE:Do you have any comments or ideas for this project?

Eventually the PIC32 is already more powerful than 68000, but of course does not have interface for 16 MByte RAM, and is not comfortable for assembler, or it is not used much at all.

68SEC000 is still interesting these days, small SMD chip, and only needs 15mA. But RAM chips need a lot of power, actually. Eventually I want to emulate this using a PIC32, and serial RAM ICs. To reduce power consumption. But a lot of work I think.

I'm not sure what do you mean by the interface for 16MByte RAM, but PIC32 has 8/16-bit PMP (Parallel Master Port) module that can be used to communicate with external memory, LCD and other parallel devices.

Really looking forward to the completion of this project!
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Re: 68000 computer, including PIC RAM bootloader

Postby Brian Griffin » Fri Jun 01, 2012 2:11 pm

I pretty like retro hardware, and including one of these things. Keep it up.

In Malaysia, it's pretty hard to get those chips, or I will have to go to the scrapyard and hunt for these things. :)
PIC - UIC00B from Cytron (replacement for my broken PICKit 2), Pickit 3, MikroC for PIC
dsPIC - MikroC for dsPIC, mikromedia board (dsPIC33)
AVR - AVR Dragon
Parallax - Prop tool
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Re: 68000 computer, including PIC RAM bootloader

Postby takao21203 » Fri Jun 01, 2012 6:26 pm

OK here an update, PCI backplane + one card together with 68000 chip.

I will work on this project if I find some time.

137211889_big.v1338498731.jpg
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Re: 68000 computer, including PIC RAM bootloader

Postby Brian Griffin » Fri Jun 01, 2012 7:28 pm

Hmm. Cool. The huge chip is such rare stuff.

Btw, what's that thing that is on the box with the 7-seg display? It said "Elektronika 01" and "Kvazar". (Pardon my limited Russian - I only learn the alphabets from my neighbor who studied in Moscow before...) :)
PIC - UIC00B from Cytron (replacement for my broken PICKit 2), Pickit 3, MikroC for PIC
dsPIC - MikroC for dsPIC, mikromedia board (dsPIC33)
AVR - AVR Dragon
Parallax - Prop tool
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Re: 68000 computer, including PIC RAM bootloader

Postby takao21203 » Sat Jun 02, 2012 8:03 am

yes CERDIP is not manufactured anymore since the late 1980s at least not for consumer chips.

these are from 1985 still have 20 or 30 of around here.

They actually figured out failure rates for manufacturing are higher for CERDIP than for plastic,
so it was not prefered anymore to use.

The gadget on the left is a VFD clock from Ukraine, bought this from eBay, when I saw it on a soviet vintage electronics website. This one was developed in the mid 1990s. And it's quite obscure, has a reset button, after power up does not start up correctly. A switch to stop/hold time as well, and to change between hours/minutes, or minutes/seconds.
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