MC68000p system from scratch - Page 1
Forum section: electronics / projects

author: haxtormoogle
author_rank: Newbie
timestamp: September 25, 2013, 12:14:03 am
content: I always wanted to learn how the classic macs were designed and how they worked. (Mac plus for the win). I was trying to figure out how modern systems are designed but it feels like everyone is telling me "buy this chip, wire it this way because we told you so, you need this chip set or you cant use this processor, No we are not telling you how it works. "I figure we can't keep moving forward without learning how things worked in the past, you cant learn from the mistakes made or what worked well.So I picked up several books on system design based on the 68000 architecture and have been reading.I want to make a modular system that can be upgraded easily if I find something new to test out.This is what i have so far figured out. (large image)http://wtfmoogle.com/wp-content/uploads/2013/09/68kbrd.pngSimple eeprom interface with IRQ and IRQ acknowledge.I've gotten some crazy ideas I want to experiment with. Replace all roms, and ram with Fram and have a system that can be powered off and keep its statusSo anyone got any tips or tricks I can use?Should I add DMA support?

author: senso
author_rank: Frequent Contributor
timestamp: September 25, 2013, 01:07:48 am
content: Dont forget to invoke all the power supply pins, and the G(enable) of IC5 is not connected to anywhere.

author: free_electron
author_rank: Super Contributor
timestamp: September 25, 2013, 05:14:40 am
content: Couple of things : your machine has no ram...You cant suspend to fram as the comtemts of the cpu registers will be lost you would need a core that can preserve its co te ts while the clock is supsended.That way you could freeze the system by stoppingtxhe clock. I don't think this is possible with the 68k...

author: andersm
author_rank: Super Contributor
timestamp: September 25, 2013, 05:30:02 am
content: Try finding a copy of the book68000 Microcomputer Systems: Designing and Troubleshooting, it covers the designing of a 68000-based system from scratch. It should really help get vital parts such as the bus interface right.

author: amyk
author_rank: Super Contributor
timestamp: September 25, 2013, 10:20:17 am
content: The regular 68k and even the CMOS version is dynamic, it has a minimum clock frequency.There is a MC68SEC000 which is a static core.

author: zapta
author_rank: Super Contributor
timestamp: September 25, 2013, 04:22:55 pm
content: Whatever you do, make sure you have software support for it (operating system, compiler, etc). Otherwise it will be useless silicon. I would start with the software selection.

author: Fraser
author_rank: Super Contributor
timestamp: September 25, 2013, 05:27:25 pm
content: I wanted to learn about repairing 68000 series based SBCs.I purchased an old Atari 520ST as that is basically a MC68K application note design on which I could experiment. It cost me $30 as it had a faulty FDD. Everything else worked fine and the FDD just needed a head clean. For the money you get a 68K CPU, ROM, RAM, PSU, keyboard and peripheral interfaces. Perfect for experimentation, and at least you know it worked before you changed something ! Its well built and a neat single PCB to play with.I recommend buying one to learn about building a 68K based computer. The Atari ST series service manuals and schematics are freely available and helpful in understanding the design.I also bought a pile of MC68000 series books and found them cheaply on ebay. Sadly I never found one of the old development boards that were sold for educational purposes. Hence the Atari ST purchase.I purchased the following books:The Motorola MC68000 - An introduction to processor, memory and interfacing _Jean BaconUsing and Troubleshooting the MC68000 - James W CoffronMicroprocessor Systems Design - 68000 Hardware, Software, and Interfacing - Alan ClementsTroubleshooting Microprocessor Based Systems - Allan H Robbins / Brian LundeenThe Handbook of Troubleshooting Techniques for Microprocessors and Microcomputers - Robert G Middleton.I could not get the book that has already been recommended, "68000 Microcomputer Systems: Designing and Troubleshooting" , as the used prices are eye watering !

author: nctnico
author_rank: Super Contributor
timestamp: September 25, 2013, 05:58:49 pm
content: It depends a bit on what you want. IMHO buying a complete computer defeats the purpose of learning how a system works. The picture below shows the first SBC I ever build. Its also the first PCB I created using schematics and PCB software so the layout is very crappy (at that point it didn't occur to me the EPROM and SRAM have a similar pin layout so it would have been much better to put them next to each other). Anyway its built around a 4MHz Z80, EPROM and SRAM with a couple of registers to create 8 bit outputs and bus drivers to create inputs. I think I also have a pre-decoded address/data bus for easy interfacing with more complicated peripherals. Later on I used it to control a frequency counter.

author: andersm
author_rank: Super Contributor
timestamp: September 25, 2013, 07:31:43 pm
content: Quote from: Aurora on September 25, 2013, 05:27:25 pmOccassionally reasonably-priced copies pop up. I think my copy cost $20-$30, but I had to keep an eye out for several months.

author: Fraser
author_rank: Super Contributor
timestamp: September 25, 2013, 10:57:37 pm
content: The S100 type 68K SBSs are well known to my IT colleagues but I was unable to find one to buy. I was hoping to stumble upon the Motorola Educational SBC but alas it is likely long lost to the landfill or collectable, so rare ?I have learned to respect the capabilities of this old microprocessor series. It may not have the performance of the more recent offerings to the computer industry, but I was surprised to find how wide spread the 68K and its offspring has become over the years. As an example I have been repairing a US$27K thermal camera from 1997 that uses an MC68340-16 main processor with a KU80C186-20 co-processor ....an odd pairing I thought, but then I read of the 80C186 used in the 'TUBE' Co-processor for the BBC Master computers !The MC68000 series of processors is certainly of interest as you never know when you will stumble upon one, in one guise or another. I am also very familiar with the MC6809, MC6502 and Z80 so I am showing my age, but at least I could program them in Assembly language.I have lost that knowledge over the years though..... I can't even write code for a PIC these days, but then I haven't really tried

author: haxtormoogle
author_rank: Newbie
timestamp: September 28, 2013, 01:52:26 am
content: Got a ton of the procs dirt cheep on ebayOne of the books in my collection is that 68000 microcomputer systems designing and troubleshooting book by Alan d. wilcoxI also have microcomputer systems design 68000 hardware, software, and interfacing second editionReading my brains outOne thing im not too sure on is if I should implement a CDMA controller or not.