Last visit was: Fri Sep 18, 2020 8:33 pm
It is currently Fri Sep 18, 2020 8:33 pm



 [ 6 posts ] 
 Experience with 68SEC000? 
Author Message
User avatar

Joined: Tue Jul 23, 2019 5:55 pm
Posts: 4
Location: Hixson, TN USA
First time poster!

I'm starting my first 16-bit project (I designed an 8-bit 65C02 computer last year). Since I plan on using some FPGA's, I thought about going with the 3v3 version of the 68K (68SEC000). Plus, they are still pretty cheap to get.

Anyone work with that chip? None of the design documents I've found seem to mention it. It has a "true" A0 whereas many documents mention that an original 68K doesn't have an A0 pin. All of them seem to use the /LDS and /UDS.

Anyway, I was wondering if anyone knew of any gotchas I should be aware of when using this chip compared to the more traditional 68K's.

Thanks!


Tue Jul 23, 2019 6:24 pm

Joined: Wed Jan 09, 2013 6:54 pm
Posts: 1440
Welcome! Let's see if we can help - either way, it will be interesting to hear about your progress.


Wed Jul 24, 2019 6:39 am

Joined: Wed Jan 14, 2015 2:56 pm
Posts: 8
Location: South Wales, UK
I've not used the 68EC000 version myself but looking at the datasheet it looks like A0 is used along with the LDS and UDS lines.

https://www.nxp.com/docs/en/reference-manual/EC000UM.pdf

Quote:
During operation in the 16-bit mode, byte operations can occur on either D15–D8 or D7–D0,depending on A0. If A0 is zero, the upper byte is used and UDSB is asserted. If A0 is one,the lower byte is used and LDSB is asserted. For word and long-word operations, A0 is always zero, data bits D15 through D0 are used, and both LDSB and UDSB are asserted.For long-word operations, data is transferred in two bus cycles with A1 indicating which half of the long word is being transferred. The actual order of the long-word halves is instruction and address-mode dependent.


Wed Jul 24, 2019 10:57 am
User avatar

Joined: Tue Jul 23, 2019 5:55 pm
Posts: 4
Location: Hixson, TN USA
I haven't seen that PDF yet. I will add it to my collection and study it as well.

Thanks!


Wed Jul 24, 2019 12:33 pm
User avatar

Joined: Mon Feb 03, 2020 4:08 am
Posts: 5
Location: Planet Earth, FL, USA
Oddly, I've always wanted to do something with the 68000. It's a nice CPU... so resurrecting this older thread seems appropriate. I've done a fair amount with the 65C02 over the past 7 years (spare time wise). I'm still working on those projects, but I'm still interested in doing a 68K project.

I've found a fair amount of technical info (docs) recently and have ordered some QFP64 20MHz M68SEC8000 CPUs. I'll need to do some breadboard prototype first, then start to figure out the 16-bit memory and I/O as I progress.

Did you (CBMEEKS) ever get around to building something up around the 68K?

_________________
Regards, KM
https://github.com/floobydust


Mon Aug 10, 2020 12:58 am
User avatar

Joined: Mon Feb 03, 2020 4:08 am
Posts: 5
Location: Planet Earth, FL, USA
In my recent searching, I've come across the retrobrewcomputers.org site. Most interesting.... I found the Tiny68K system that Bill Shen has put together. He still has some available so I ordered two (my son wants one), fully assembled and tested. It came with a Motorola 68000 running at 12MHz, a Motorola 68681 DUART, an Altera EPM7128SQC100-10 FPGA for glue logic, two 256KB Serial EEPROMs (selectable via jumper), a 16MB 72-PIN DRAM module and a 64MB Compact Flash card configured and running CP/M-68K version 1.3. He also included a USB-Serial adapter. All for $50 plus $5 shipping. It's a nice 2-layer board with a fair amount of SMT parts (pats on both sides)... and the build quality is excellent. Link is:

https://www.retrobrewcomputers.org/doku ... ny68k_rev2

I have this (Tiny68k) running now... even followed his (online) instructions to build up a new CF Card complete with zero issues. The board uses the serial 256KB EEPROM to hold the BIOS/Monitor and the FPGA does everything else... provides DRAM refresh circuitry, all I/O and memory decoding.. and loads the contents of the serial EEPROM into memory on boot up, then releases the CPU to boot into the monitor.

But... back to the main topic. I think the Tiny68K will serve well for doing some development work, as it's fully configured with the 68K Assembler/Linker, C compiler and CBasic compiler. It all works... but using ED for editing source isn't happening. The board does support Kermit for file transfer and I've got that working using Serial on OSX. So for now... I have a working 68K system that I can do dev work and have Easy68K running on a Win7 VM for developing code as well.

I have some processors arriving tomorrow... 20MHz 68SEC000 in QFP-64 package. It will probably be a while before I get to putting a breadboard system together, but for now I have a working 68K system with an OS that I can use to start learning some assembly language on.

Side note: I picked up a couple 5-volt wall-wart supplies from Mouser to power these... as they DC connector is a 2.5mmx5.0mm... less than $13 each.

_________________
Regards, KM
https://github.com/floobydust


Thu Aug 13, 2020 2:04 am
 [ 6 posts ] 

Who is online

Users browsing this forum: CCBot and 0 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group
Designed by ST Software