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Processor Choice

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FlyingJester

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Jun 2, 2011
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4
Hey

I am working on some simple homebrew designing, and I was wondering how some of the old processors I have compare to each other. I have a Z8 romless, 65C02P, and an Intel D-8088-2. Are these even comparable performance wise? I think I've heard the Z8 is modified harvard structure, unlike the other two (and most cpus) which are von neumann (right?), but all I'm really woried about how they will perform. I don't want a CPU that is blindingly fast for the rest of the project, but I want one that still performs well.

thanks
 
The 8088 and the 65C02 are what I'd call microprocessors and the Z8 is a microcontroller. The latter is far from general purpose although it would be the simplest of the three to build a project with (yes, it is Harvard architecture with separate data and program memories). The Z8 has a few on-chip peripherals, but you won't find much pre-written code for it, as it sees almost all of its use in embedded applications.

The 65C02 architecturally belongs to the mid 1970s and is an 8-bit CPU with some serious design compromises and has a 65K byte unified address space. The 8088 is a second-generation CPU with a 16-bit ALU (and an 8-bit BIU) and can address (in maximum mode) 1MB memory and 64K I/O. Since the 8088 outputs a status signal that indicates which segment is being used for memory access, it could also easily be turned into a Harvard architecture processor. I'm not sanguine about doing the same thing with the 65C02, though there were microcontroller versions of that chip.

It's easier to find chips that work with the 8088's I/O protocol and the 8088 probably has the largest program base. Both the 8088 and the 65C02's program bases are tied to definite system implementations (the 65C02, the Apple II/III and the 8088, the IBM PC).

As far as designing with either, it's about the same.
 
I am not sure any of those would be my first choice for a CPU. Given the choice of CPU limits the software you can run the sort of support you can get on a host, then perhaps I would be looking for a 6809, Z80 or 8080 because of the support you can get, so flex or cpm. I guess there is also 6502 software out there as well...
 
g4ugm said:
I am not sure any of those would be my first choice for a CPU. Given the choice of CPU limits the software you can run the sort of support you can get on a host, then perhaps I would be looking for a 6809, Z80 or 8080 because of the support you can get, so flex or cpm. I guess there is also 6502 software out there as well...
Click to expand...

No, I certainly wouldn't, but the question was asked.

Any of the choices are woefully underpowered in comparison to even the simplest of today's microcontrollers. And you can get ready-made development kits for those. Some, such as the eZ80 will even run CP/M. Heck, you could probably write an emulator for any other vintage CPU and still have cycles to spare.

This is where the-clock-speed-is-everything thinking really falls on its face. A 4MHz Z80 is nothing like even a 4MHz PIC (as an example)--the PIC pipelines instructions and pretty much executes all instructions in a single cycle. There's no multi-cycle memory latency or multi-clock instruction cycle to slow things down.

But if one wanted a vintage design experience with all of the design headaches and lack of performance, I'd probably start with an 8080 or 8008 CPU.
 
Underpowered is relative. At the very beginning I was also considering using an original Pentium I have, but I deemed it to advanced for this project.

I was also considering running one as the cpu and one for driving graphics, which would of course be complicated.

I was seriously considering the 65C02, but I think I'll do a little research on the 8080 now. And leave the Z8 for another day.
 
You should also take a look at the 8085. It's a little easier to set up than an 8080. The 8085 only requires +5v, instead of +5, -5 and +12 for the 8080. And the 8085 has a few more built-in features, like a clock oscillator. You can set up a working system with fewer chips.
 
tomasont said:
You should also take a look at the 8085. It's a little easier to set up than an 8080. The 8085 only requires +5v, instead of +5, -5 and +12 for the 8080. And the 8085 has a few more built-in features, like a clock oscillator. You can set up a working system with fewer chips.
Click to expand...

And if you don't want to build the whole board yourself, or you want some direction in getting started, I'm working on an 8085 SBC:

http://www.glitchwrks.com/8085projects/

I really like the 8085 for its simplicity and bus structure. The multiplexed bus lets you add 256 I/O port devices with 16 data lines, which was really convenient for my SBC design. If you're interested in some version 2 boards, I do have two left (they're not posted to the projects page yet, but they support 64K memory in 32K RAM and up to 32K ROM, or 64K RAM with external ROMs).

I'm also working on a generic 8-bit bus structure for hobbyist projects with a friend of mine. It's basically a bus standard and option cards that work with it. There will be a few premade standard CPU cards (8085 and 6502 to start with), but the same RAM, ROM, and I/O cards will work with all of them. That's a little ways off though...still in the design phase.
 
FlyingJester said:
Underpowered is relative. At the very beginning I was also considering using an original Pentium I have, but I deemed it to advanced for this project.

I was also considering running one as the cpu and one for driving graphics, which would of course be complicated.

I was seriously considering the 65C02, but I think I'll do a little research on the 8080 now. And leave the Z8 for another day.
Click to expand...

Graphics of any quality requires some horsepower. The Z80, 6502 and 8088 can do simple graphics okay, but there is the matter of a graphics controller, even if it's a MC6845. An 8080 might be pushing matters; doing graphics with a Z8 would be a nightmare that I wouldn't want to deal with.

Z80s are easy to use, available and cheap. If you want vintage, that's a pretty good start.

And by all means, have a look at some of Andrew Lynch's work (ion this forum). He offers quite a range of project kits.
 
Chuck(G) said:
Graphics of any quality requires some horsepower. The Z80, 6502 and 8088 can do simple graphics okay, but there is the matter of a graphics controller, even if it's a MC6845. An 8080 might be pushing matters; doing graphics with a Z8 would be a nightmare that I wouldn't want to deal with.

Z80s are easy to use, available and cheap. If you want vintage, that's a pretty good start.

And by all means, have a look at some of Andrew Lynch's work (ion this forum). He offers quite a range of project kits.
Click to expand...

How complex of graphics are you thinking about? Apple IIe can do some pretty decent stuff using just the 6502 to do graphics PLUS main processing tasks. If you did main processing on the 8088, and pawned off graphics work to the 6502, you could get some nice smooth graphics going.
 
Well, there's nothing inherent graphically speaking in the 6502 that you couldn't also do with a Z80.

Andrew, if I remember correctly, also has a NEC 7220 project going for some more advanced graphics.
 
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