Author Topic: For a vintage computer project, which processor is easier to use?  (Read 16833 times)

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Offline C

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Re: For a vintage computer project, which processor is easier to use?
« Reply #25 on: July 07, 2017, 10:58:08 pm »
68000 works from no memory and times out when no memory exists.
Unless you ground DTACK.

DTACK Grounded

And if you do so you have a lot less capable of system for a very small savings.
Easy to replace hardware with software at a cost of a slower system.
Easy to leave out hardware and get a less capable system.
Also not hard to save when you have more than one CPU in a system.
 

Offline eugenenine

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Re: For a vintage computer project, which processor is easier to use?
« Reply #26 on: July 07, 2017, 11:45:47 pm »
IIRC the VME bus was a standard built around the 68k.  You make a backplane then plug in processor boards, memory boards, etc.
 

Offline Bruce Abbott

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Re: For a vintage computer project, which processor is easier to use?
« Reply #27 on: July 08, 2017, 01:01:24 am »
And if you do so you have a lot less capable of system for a very small savings.
Easy to replace hardware with software at a cost of a slower system.
Easy to leave out hardware and get a less capable system.
Also not hard to save when you have more than one CPU in a system.
OP asked which processor is easier to use, not which one can go faster or have more CPUs in a system.

It has been suggested that the 68000 is harder to use than the 8088 because it has a 16 bit bus and requires generation of a DTACK signal. But if ease of use is the goal then you could use a 68008 (8 bit data bus) and ground DTACK. Of course all your memory and peripherals would then have to run at 2MHz bus speed, but that's not a problem for modern chips. Less expandable than it could be? Sure. But easier.
 

Offline eugenenine

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Re: For a vintage computer project, which processor is easier to use?
« Reply #28 on: July 08, 2017, 01:44:37 am »
OP asked which processor is easier to use, not which one can go faster or have more CPUs in a system.


6502, has the ease of hardware interfacing of the 8088 and the easier coding of the 68k.
 

Offline westfw

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Re: For a vintage computer project, which processor is easier to use?
« Reply #29 on: July 08, 2017, 07:22:36 am »
Quote
keep in mind that *existing software* is also a metric in my consideration.

Oh.  Well in that case, I think you're screwed.  Most of the 68k systems of that era (or at least most of the ones that have had any software preserved) has highly proprietary operating systems that were heavily dependent on "elegant" but proprietary custom hardware.  (I'm thinking of Amiga, Macintosh, and the early unix workstations (SUN-1 !))

Go with the 8088 (or get a NEC V-20, for some near additional capabilities and nearly identical hardware.)  No need for an 8087 (I'm not sure why you included that, since the 68k doesn't have an FPU.)  MSDOS and the PC BIOS are at least designed for portability across "similar" hardware, and there has been continued development of things like FreeDOS.

Other possibilities for retro-computing with some hope of running old software include a Z80 running CP/M or a 6809 running OS-9. (I'm particularly fond of this recent 4-chip Z80 hardware: https://hackaday.io/project/19000-a-4-4ics-z80-homemade-computer-on-breadboard - it's been made to work by several people in several formats, and is currently running CP/M, and Forth, and "ROM" BASIC.  The basic design might work for other CPUs, too...)  (Hmm.  There was an OS-9 for 68k; I'm not sure if it ever got much traction...)

6502 has similar problems to 68k  - popular software (C64, Apple ][, Atari) was dependent on custom hardware.  In general, when you look at classic personal computers, there was a LOT of custom hardware, and most of the "really clever" programming came from manipulating that hardware, rather than being generic xx-cpu software.  (It's a bit depressing.)

(Keeping in mind that while most of that "personal computer revolution" was happening, I was off programming mainframes and not paying THAT much attention.  But that's how I remember things...)
 

Offline technix

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Re: For a vintage computer project, which processor is easier to use?
« Reply #30 on: July 08, 2017, 01:30:48 pm »
Also if I want to build a PC XT compatible there are a lot of reference material and test code out there. The system design can be checked against the source code of DOSBox. The BIOS code can be checked against the released original IBM BIOS as well as code from SeaBIOS and coreboot projects. And a test boot of vanilla MS-DOS 6.22 can be used to exercise various components.
 

Offline Bruce Abbott

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Re: For a vintage computer project, which processor is easier to use?
« Reply #31 on: July 08, 2017, 03:51:55 pm »
if I want to build a PC XT compatible
Then use an 8088. Why even consider 68000 if that's what you want to do?

 

Offline amyk

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Re: For a vintage computer project, which processor is easier to use?
« Reply #32 on: July 08, 2017, 04:38:35 pm »
Why not a 486/AT clone, then you can actually run more interesting software: http://www.s100computers.com/My%20System%20Pages/80486%20Board/80486%20CPU%20Board.htm
 

Offline technix

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Re: For a vintage computer project, which processor is easier to use?
« Reply #33 on: July 08, 2017, 04:44:30 pm »
if I want to build a PC XT compatible
Then use an 8088. Why even consider 68000 if that's what you want to do?
I have the 8088 already, but got a bit stumped at how to hook up 8088, 8087, 8288 and 8284 into the actual CPU complex, how to hook the CPU complex to the platform controller CPLD, how to interpret the signals from the CPU complex, and how to make the CPLD-based chipset work.
 

Offline legacy

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Re: For a vintage computer project, which processor is easier to use?
« Reply #34 on: July 08, 2017, 04:59:28 pm »

 

Online Nusa

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Re: For a vintage computer project, which processor is easier to use?
« Reply #35 on: July 08, 2017, 05:53:09 pm »
You're mostly asking questions that are easily answered with basic search skills.

Assemblers for all of the above? Easily found. Including plenty of cross-assemblers written in portable C, since these chips predated the PC and binaries were often compiled with whatever computer was available.

How to build a 8088 based XT clone? Easily found, including schematics for single-board computers. Ditto for the other CPU's mentioned.

If the real goal is simply to have a working XT clone, the cheapest route is still to just buy one. Plenty of working antiques out there for not that much money. If you want original glue logic IC's, look for XT/XT clone motherboards, as is/for parts ones will be cheaper. Often the chips are even socketed.
 

Offline amyk

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Re: For a vintage computer project, which processor is easier to use?
« Reply #36 on: July 09, 2017, 03:07:32 am »
You're mostly asking questions that are easily answered with basic search skills.

Assemblers for all of the above? Easily found. Including plenty of cross-assemblers written in portable C, since these chips predated the PC and binaries were often compiled with whatever computer was available.

How to build a 8088 based XT clone? Easily found, including schematics for single-board computers. Ditto for the other CPU's mentioned.

If the real goal is simply to have a working XT clone, the cheapest route is still to just buy one. Plenty of working antiques out there for not that much money. If you want original glue logic IC's, look for XT/XT clone motherboards, as is/for parts ones will be cheaper. Often the chips are even socketed.
You can even get the schematics of the real thing: http://www.minuszerodegrees.net/manuals.htm#IBM
 

Offline westfw

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Re: For a vintage computer project, which processor is easier to use?
« Reply #37 on: July 09, 2017, 06:02:58 am »
(It's one of the things that annoyed me about that TV series "Halt and Catch Fire."  The trope that the IBM PC was this secret bit of high technology that it took some super-hackers to "reverse engineer."  When in fact the IBM was a horribly BORING hardware design, most of which was published.  ("published" but not at all "open source."  IIRC, the hard part was finding engineers who hadn't been "contaminated" by looking at any of the published material.)

There were even x86-based personal computers that ran MSDOS, but were NOT IBM-PC compatibles (eg the HP-150; the first PC I owned.  (Not counting the CP/M system that never got more than half-assembled.))
 

Offline NivagSwerdna

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Re: For a vintage computer project, which processor is easier to use?
« Reply #38 on: July 09, 2017, 10:09:22 am »
I have some vintage computer projects on the sketch boards for a while, but I am still undecided which to pursue first. Which of the two would be easier to use in your opinion: Intel 8088 + Intel 8087, or Motorola MC68HC000? Aspect to be consider includes the simplicity of the system design, and availability of compilers, tools, libraries and existing programs.
68000

What is your end goal?
 

Online rstofer

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Re: For a vintage computer project, which processor is easier to use?
« Reply #39 on: July 10, 2017, 05:07:40 pm »
In my view, the EASIEST chip to use is the Intel 8085.  It is a superset of the 8080 but is static CMOS so there is no minimum clock rate.  Back in the early '80s, I built several projects with this chip and its brethren.  Given the availability of static CMOS RAM in 64kx8, the memory system is quite simple.

You can run CP/M on such a system with a little effort.  Interfacing a Compact Flash device is quite easy.

CPU + AddressLatch + CMOS RAM + EEPROM + Memory Map Logic (map EEPROM into memory space at startup, map it out when some condition occurs) + Address Select Logic for IO devices + a couple of UARTS and you're good to go.

Or, just buy one of the Zilog eZ80F91 boards - they run at 50 MHz and have all the required memory.  Add a daughter card containing the Compact Flash and a couple of UART->USB devices (or one of the newer quad UART->USB) and you're up and running on CP/M with 16 logical drives.  CP/M RIPS at 50 MHz.

« Last Edit: July 10, 2017, 05:17:25 pm by rstofer »
 

Elf

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Re: For a vintage computer project, which processor is easier to use?
« Reply #40 on: July 11, 2017, 05:10:59 am »
[...] but is static CMOS so there is no minimum clock rate.
WDC's 65C02 also has this helpful property.

Or, just buy one of the Zilog eZ80F91 boards - they run at 50 MHz and have all the required memory.
Plus Ethernet with a BSD sockets implementation. Definitely nice little boards, although I wish the modules were a bit cheaper.

I didn't realize it was easy to get CP/M going on them. Interesting!
 

Offline technix

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Re: For a vintage computer project, which processor is easier to use?
« Reply #41 on: July 11, 2017, 07:05:24 am »
A lot of you are suggesting 68000 for this vintage computer project. I don't have the required peripheral chips yet (and I doubt whether my 8-bit USB and Ethernet chips would work on a 16-bit bus) so please suggest chips for UART, display output stack, Ethernet and USB-OTG. Or is there any CMOS variant of 68008 (which have a native 8-bit bus)
 

Online Nusa

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Re: For a vintage computer project, which processor is easier to use?
« Reply #42 on: July 11, 2017, 07:44:34 am »
A lot of you are suggesting 68000 for this vintage computer project. I don't have the required peripheral chips yet (and I doubt whether my 8-bit USB and Ethernet chips would work on a 16-bit bus) so please suggest chips for UART, display output stack, Ethernet and USB-OTG. Or is there any CMOS variant of 68008 (which have a native 8-bit bus)

The 68008 in any varient hasn't been manufactured for over 20 years, nor was it ever a big seller. I don't know how easy it is to find old stock.

Using a 16-bit data bus on an 8-bit device is trivial. You just use the lower 8 bits. You do, of course, still need the full address decoder for the chip select line.
 

Offline legacy

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Re: For a vintage computer project, which processor is easier to use?
« Reply #43 on: July 11, 2017, 07:46:15 am »
 

Offline legacy

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Re: For a vintage computer project, which processor is easier to use?
« Reply #44 on: July 11, 2017, 07:54:41 am »
the EASIEST chip to use is the Intel 8085

yup, 6800 : 68hc11 = 8080 : 8085
I believe  :D
 

Offline technix

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Re: For a vintage computer project, which processor is easier to use?
« Reply #45 on: July 11, 2017, 09:09:49 am »
Rounding up again.

* Among the two options I mentioned, 68HC000 is easier to use.
* It is okay to use 8-bit peripherals with a 16-bit bus, by hooking the chips to just the low byte. Drivers have to be made flexible enough to accommodate this.
* 2MB of SRAM is enough for a 68000 retrocomputing platform.
* When using 68000, forget existing code.
 

Offline NivagSwerdna

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Re: For a vintage computer project, which processor is easier to use?
« Reply #46 on: July 11, 2017, 09:28:16 am »
I have some vintage computer projects on the sketch boards for a while, but I am still undecided which to pursue first.
This thread seems to be oscillating wildly.  What do you actually aim to achieve?
If you want cool and vintage... Cosmac 1802 (if it was good enough for the moon landing), 6502 (PET) or Z80 (Jupiter ACE?).  1802 and 6502 are very simple especially with SRAM.  Z80 slightly more complex if you use DRAM. 
For the time 6800 and the 68000 were cool, the 68000 being used in quite a few communications systems.  The 6800 was surplanted by the 6502 which was much much cheaper. TBH they are just a bit dull IMHO. Also 8080, 8085... yawn... what came after was far cooler.
Or... at a tangent... how about re-creating a classic arcade game (they often had multiple processors)... something along the lines of... http://www.fpgaarcade.com/replay/

« Last Edit: July 11, 2017, 09:29:54 am by NivagSwerdna »
 

Offline Fungus

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Re: For a vintage computer project, which processor is easier to use?
« Reply #47 on: July 11, 2017, 09:47:30 am »
Have you studied ether of the two?

I see the 8088 as an 8-bit computer stretched to a 16-bit instruction set and a 1 meg address space, Segmented memory.
From a software side try to create an array with more then 64k of data

68000 is 32-bit with a 16-bit external bus. The big cripple was that the 68 pin chip needed more pins to get 8 more address lines out of chip.

Not if it's a 68008.  :)

PS: Z80 is probably easiest.

If the real goal is simply to have a working XT clone, the cheapest route is still to just buy one.

Building an XT clone is a LOT of work.

I wouldn't build anything with the goal of "running old software". Nobody will be impressed and there's emulators for that.

If I was going to build a retro computer I'd dream up a new one.
 

Offline westfw

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Re: For a vintage computer project, which processor is easier to use?
« Reply #48 on: July 11, 2017, 09:52:54 am »
Quote
is static CMOS so there is no minimum clock rate.
This is also true of the current CMOS Z80 chips (Z84c00) (and I think of a lot of the more recent CMOS versions of most "classic" chips, like the 80c88 you can get from Intersil (sticker shock!), the 80c18x (might be an interesting choice; has some built-in features that make systems easier to build, but will still run MSDOS), etc)
 

Online rstofer

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Re: For a vintage computer project, which processor is easier to use?
« Reply #49 on: July 11, 2017, 02:35:38 pm »
It's pretty tough to stop this thread from oscillating when the original topic seemed to be 'vintage' and then Berkeley Sockets comes up.

It comes down to a question of "how vintage?".  Mid '70s or mid '80s (perhaps mid '90s).  To me, the Altair 8800 ('75) defines 'vintage'.  Everything else is a "Johnny come lately".  OK, I stretch it to maybe include the Apple II and certainly the 8085 (6502, 1802, Z80).  The introduction of the IBM PC in 1980 pretty much wiped out the idea of 'personal computing' and started 'just commercial computing'.  Anybody could run an IBM PC.  With the Altair, it took a certain amount of understanding.  The Apple II was a lot easier to understand.

So, which vintage are we talking about?

 


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