Motorola m68k question: mc68EC020 vs mc68020? - Page 1
Forum section: electronics / general

author: legacy
author_rank: Super Contributor
timestamp: May 25, 2018, 08:48:14 pm
content: The M68EC020 processor has been used as the base processor in some Amiga models most notably the A1200, and the primary difference between the MC68EC020 and the MC68020 is that it has a 24bit address bus.Here I happen to have a board with an MC68EC020RC20 on the top of the socked, and I replace it with an MC68020RC25 the board doesn't start.Everything is tested and known of being working, e.g. the MC68020RC25 works for another board.The starting address is below the 24bit address space, it's located at 0x0080.0000, as well as the stack is located at 0x0000.1000What could be wrong?

author: MT
author_rank: Super Contributor
timestamp: May 25, 2018, 11:13:58 pm
content: A shoot in the dark, IRQ, Buss REQ etc logic using address bits above the 24'th?Assuming "internally" 020 and EC020 are exactly the same. Amiga CD32 games console used EC020.

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 26, 2018, 01:51:40 am
content: Old memories and some digging up pointed to some differences apart from the address bus width. They have a somewhat different way of handling bus arbitration. The 68EC020 doesn't have a bus grant acknowledge signal, whereas the 68020 does. I really can't remember all the subtleties of the 68k series, but I think this may explain why the 68020 appears to get stuck (assuming that in the package you use, they are pin-to-pin compatible otherwise).Look for 'BUS GRANT ACKNOWLEDGE' in the datasheet, and go from there. May be a clue as to what's wrong. It might just be a matter of pulling up this pin on the 68020 and not leave it floating, but I'm not sure. You may have to add some glue logic. Much too old memories. You have to go from there. Good luck.

author: legacy
author_rank: Super Contributor
timestamp: May 26, 2018, 10:53:57 am
content: Thanks, guys!They should be pin-to-pin compatible. I will check the UM in details.

author: legacy
author_rank: Super Contributor
timestamp: May 26, 2018, 01:08:08 pm
content: So, the problem is: even though they both come in a 13x13 PGA package, they do not pin compatible.Even Vcc and GND are different

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 26, 2018, 03:21:44 pm
content: So you're lucky if you didn't fry anything.Why do you want to "upgrade" to a 68020? I don't think there is any performance difference per se, but I think the 68020 can run at higher frequencies, so that may be one reason? Another reason could be a problem of availability (in which case you can find some 68EC020's on eBay).If you really want a 68020, you'll probably have to design an adapter board. Since it's a PGA package, it shouldn't be too difficult to do.

author: madires
author_rank: Super Contributor
timestamp: May 26, 2018, 03:37:20 pm
content: IIRC, the EC types have no MMU.

author: legacy
author_rank: Super Contributor
timestamp: May 26, 2018, 05:55:08 pm
content: Quote from: SiliconWizard on May 26, 2018, 03:21:44 pmOn the CPU board there is a current limiter. Everything got re-tested and it is working, we are luckyQuote from: SiliconWizard on May 26, 2018, 03:21:44 pmAesthetically I prefer gold-cap chip, but there is also another reason: I don't have a M68EC020RC25 here, while I have an M68020RC25.The PLL I have on the CPU board divides a 50Mhz click by2 or by4: 25Mhz, 12.5Mhz.Quote from: SiliconWizard on May 26, 2018, 03:21:44 pmBusy with other project. Lazy reason, say

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 26, 2018, 06:20:03 pm
content: There is one here that should fit:https://www.ebay.com/itm/MC68EC020RP25-MOTOROLA-100PIN-PLASTIC-PGA-25MHZ-32BIT-PROCESSOR-NEW/322255928517?epid=1831087451&hash=item4b07f33cc5:g:2doAAOSwxg5X0eQYNo gold cap though.

author: legacy
author_rank: Super Contributor
timestamp: May 26, 2018, 07:20:40 pm
content: Yup. Thanks. I will for sure buy one of these black-EC-chipI'd also have a MC68020RC33E-PGA/GoldCap, that is perfect to divide a 60Mhz oscillator by2A 30Mhz 68020 CPU. WOW!!! And the PLL accepts 60MhzBut it sounds like I have to design my own CPU board. Probably I will.I am playing with an old card, just to have a minimal working firmware, something that I can easily modify to suit future homemade boards.

author: SiliconWizard
author_rank: Super Contributor
timestamp: May 26, 2018, 07:47:07 pm
content: If you're not absolutely after a genuine CPU (but by your nickname and your questions, I'd guess you are), you could take a look at this project:https://github.com/MHeinrichs/68EC020-TK

author: legacy
author_rank: Super Contributor
timestamp: May 26, 2018, 09:39:42 pm
content: Quote from: SiliconWizard on May 26, 2018, 07:47:07 pmYup, my "legacy" nickname can't be mistakenSo kind, for the link. Thanks. It's super interesting

author: helius
author_rank: Super Contributor
timestamp: May 26, 2018, 09:46:34 pm
content: Quote from: madires on May 26, 2018, 03:37:20 pmThe MC68020 does not have a MMU to begin with. It relied on an external MMU, either the Motorola MC68851, or a vendor-specific chip like the Sun-3 MMU. It's true that the 68030 and 68040 EC types had the MMU deleted, though.

author: legacy
author_rank: Super Contributor
timestamp: May 26, 2018, 09:52:24 pm
content: oh, and the 68040 is perfectly pin-to-pin compatible with 68EC040 and with 68LC040, as well as 68060 is perfectly pin-to-pin compatible with 68EC060 and with 68LC060.040: it was a trick used to load Linux on Apple LC475 (and Performa? maybe), a pizza box computer that comes shipped with the low cost 68LC040, but if you upgrade the chip you can run Linux or BSD.What a confusion with Motorola

author: legacy
author_rank: Super Contributor
timestamp: May 26, 2018, 09:59:29 pm
content: oh, andthispost is intriguing: a new 68020? really?

author: MT
author_rank: Super Contributor
timestamp: May 27, 2018, 12:00:08 am
content: Quote from: legacy on May 26, 2018, 09:59:29 pmworked in various positions atMostekCorporation.http://www.tekmos.com/corporate-info/management

author: legacy
author_rank: Super Contributor
timestamp: May 27, 2018, 04:48:08 pm
content: Quote from: MT on May 27, 2018, 12:00:08 amLOL. I have decided to put him on my personal list of my "mr.fantastic"-dudes