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Comment by noone_youknow | Hacker News Reader

You're right that's how most boards handle having ROM low for the first four cycles, and that's how mine does it. I use a 74LS174 hooked up just like you say.

Early in the project I did a DTACK generator similar to what you describe, but now it's handled by a GAL which allows it to be zero-wait-state in certain address spaces while supporting external DTACK for IO devices. This also allows me to easily tri-state the signal do expansion boards can generate their own DTACK.

Your side-project sounds interesting, I'd love to take a look :) is it online anywhere?

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I've got to actually start writing things down about my personal projects :)

At this point I've still just been learning about the bus timing. I've got an m68k hooked up to an 16 MHz Arduino Mega which is running the m68k at 4 MHz so I can get 4 samples per clock of the m68k (https://imgur.com/CxSlIHL). I can actually drive the CPU with the arduino since I can manage DTACK just quick enough with some inline AVR assembly.

Hit a small snag though. Turns out the 68010's I ordered are fakes.

Ended up with the same parts you did (saw your post at https://hackaday.io/project/164305-roscom68k/log/175626-fake...) (what I received: https://imgur.com/WCwRpHJ).

I was fairly naive to the fakes when I started ordering parts. I've basically ended up with all fakes. Got some Harris 80C286-25s which are fakes (internet seems to suggest they are rebadged 20 MHz parts, so at least they are the same base part (static core 286)), but I don't have the capacity to test them quite yet. I've also ended up with a 50 MHz 68030 that seems to actually be a 33 MHz 68030. Again, I can't test it yet so I'm really hoping it's not an EC part rebadged. I wanted the MMU.

Awesome :) I've played around a bit interfacing Arduino to mine too, and found I had to use AVR assembly to get the timing right.

Yep, those are exactly the same as some of the fakes I have here. Adeleparts definitely rings a bell as the source of some of mine too.

Sadly it seems to be quite common to remark the "lesser" 030/040/060s to suggest they are the fully-capable ones :( Fingers crossed yours isn't like that!

If you don't mind me asking, do you know what the fan-out capability of the "big DIP" m68k's are? I've not noticed a hobby board built around one that has bus transceivers or line drivers, but all of the boards built around things like the 8088 and 8086 have them. I know those required latches to de-multiplex the bus, but the datasheet for the Intel parts recommend line drivers and bus transceivers except for simple "minimum-mode" systems.

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