STEbus 68020

68020 processor board renovation

Keith

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Description

Renovation of a tried and tested commercial design. Not my own design!

I have several of these working boards, but no manual or circuit diagram!

It came as part of an OS/9-68K system, and tried to access the SCSI and floppy disks, but failed to boot. They are 'alive' but the system needs debugging.

Not all of the PAL chips could be read. In particular, a Texas Instruments high-speed PAL. I think this is used for address decoding but I'll have to buzz the connections with a meter.

I tried disassembling the firmware, and have an idea where the UART chip resides.

This will be quite a difficult project, with a lot of work...

Details

Programmable logic

J182/U6 24-pin AMPAL22V10PC
J182/U8 24-pin LATTICE GAL22V10-15 9040B03
J182/U9 24-pin LATTICE GAL22V10-15 9040B03
J182/U10 24-pin AMPAL22V10PC
J182/U20 24-pin LATTICE GAL22V10-15 9040B03
J182/U21 20-pin MMI PAL16L8DC

Boot ROM

I have uploaded the boot ROM files and a first go at disassembly. I'm not very familiar with 68K machine code so I can't read it like I can with 6502 and Z80 code. I don't have the time to reverse engineer it further right now, but feel free to have a go if you like puzzles.

The boot code is only 4K in size, so not a huge task but will require some thought.

Files

J182_OS9_boot_even_cs14FA.hex OS-9/68K bootstrap ROM x-hex - 77.03 kB - 02/03/2019 at 19:19		Download
J182_OS9_boot_odd_cs7961.hex OS-9/68K bootstrap ROM x-hex - 77.03 kB - 02/03/2019 at 19:19		Download
J182_OS9_boot_even_cs14FA.bin OS-9/68K bootstrap ROM octet-stream - 32.00 kB - 02/03/2019 at 19:19		Download
J182_OS9_boot_odd_cs7961.bin OS-9/68K bootstrap ROM octet-stream - 32.00 kB - 02/03/2019 at 19:19		Download
J182_OS9_boot_even_cs14FA_odd_cs7961.bin.s.txt My first attempt at disassembly to work out what it was up to. Made a good guess at where the on-board UART is, and possibly the STEbus floppy and SCSI boards. plain - 68.61 kB - 02/03/2019 at 19:19		Download

View all 6 files

Discussions

Bharbour wrote 01/03/2018 at 19:15

Good Luck on this one, the 68020 is a really nice processor. They really are not terribly complex to work with either. I designed a couple of 68020 based boards back in the early 1990s for video game applications.

Are you sure? yes | no

Keith wrote 01/03/2018 at 21:57

A bit like DRAM seems a lot more complex than SRAM, most hobbyists stick with simple synchronous CPU rather than an asynchronous 68K. I managed to master DRAM and I expect I will master the 68K family too. I've got a fully restored 68008 design, which will do a lot of the 68020 logic apart from dynamic bus sizing.

Are you sure? yes | no

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STEbus 68020

Description

Details

Files

J182_OS9_boot_even_cs14FA.hex

J182_OS9_boot_odd_cs7961.hex

J182_OS9_boot_even_cs14FA.bin

J182_OS9_boot_odd_cs7961.bin

J182_OS9_boot_even_cs14FA_odd_cs7961.bin.s.txt

Discussions

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