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Motorola 6800

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Re: Motorola 6800

#121

Post by Tor3 »

timbit42 wrote: post #108
Tor3 wrote: post #36

Earlier quoted context omitted.

The 6800 definitely is a classic, yes. The classics included at least 6800, 6502, 8080, and Z80. (To some extent 8085, but as an "expanded" 8080 the Z80 dominated.) The four of them powered the most iconic systems at the start of the microprocessor "takeover" at the end of the seventies (at the same time as I entered my electronics education). The 6800 was kind of left behind by the others eventually, but was used in…

The 1802 is neglected again.

The Cosmac ELF.. yes, I too was aware of the 1802, and there are of course other important microprocessors from that time period. But those four covered a lot among themselves - in particular the trio 6502/8080/Z80. But of course there were others. The Texas TMS9*, the 6800 already mentioned, then there's of course the 6809 (Tandy Color Computer, Dragon (basically a clone), the 6809 variant of the aforementioned SWTPC. Or we can as well find a list: https://en.wikipedia.org/wiki/Microprocessor_chronology

Re: Motorola 6800

#122

Post by deaddodo »

kjs3 wrote: post #113
deaddodo wrote: post #96

Earlier quoted context omitted.

There was also an argument that the 6501 was built as a sacrificial lamb so that when Motorola inevitably sued them, they would be able to keep the 6502 out of the case.

Do you have a source for this? I had always read the change in pin-out was initiated after Motorola went legal.

The 6501 and 6502 were developed simultaneously and the 6502 was released a month later (Aug 1975 vs Sept 1975). Both well before the lawsuit began, yet alone concluded.

Re: Motorola 6800

#123

Post by KMag »

ddingus wrote: post #83
andrekandre wrote: post #82

> It has 72 instructions with seven addressing modes for a total of 197 opcodes. noob question: why so many addressing modes?

Back then people wrote assembly language themselves. At 1-2Mhz, sometimes Khz, it was how one got performant code. Addressing flexibility makes assembly language programming practical for people to do. Check out the 6809 for a beautiful ISA and probably one of the most powerful 8 bit CPUs.

But, they pretty commonly used macro assemblers, so they could have used macros to emulate more complex addressing modes. I think code density and performance had a bigger impact than developer ergonomics on the decision to implement the more complex addressing modes in hardware instead of assembler macros.

Re: Motorola 6800

#124

Post by ddingus »

KMag wrote: post #123
ddingus wrote: post #83

Earlier quoted context omitted.

Back then people wrote assembly language themselves. At 1-2Mhz, sometimes Khz, it was how one got performant code. Addressing flexibility makes assembly language programming practical for people to do. Check out the 6809 for a beautiful ISA and probably one of the most powerful 8 bit CPUs.

But, they pretty commonly used macro assemblers, so they could have used macros to emulate more complex addressing modes. I think code density and performance had a bigger impact than developer ergonomics on the decision to implement the more complex addressing modes in hardware instead of assembler macros.

I agree with you. Both of those were a big deal given how little RAM was often available. Many systems measured in bytes!

On those, people writing programs was common.

Bigger systems, kilobytes and larger, saw the use of macro assemblers were far more common.

The first assembler I bought was a Macro assembler.

Re: Motorola 6800

#125

Post by KMag »

analog31 wrote: post #91
andrekandre wrote: post #82

> It has 72 instructions with seven addressing modes for a total of 197 opcodes. noob question: why so many addressing modes?

Another way of thinking about it was that things were done with the index registers and addressing modes, that would be represented by pointers in a language like C.

That is true, but the same could be said of even an extreme RISC ISA that only has an indirect addressing mode. Taken by itself, it doesn't help explain why late 1970s processors tended to have a lot of addressing modes.

Re: Motorola 6800

#126

Post by ddingus »

8bitsrule wrote: post #109
tgv wrote: post #98

Earlier quoted context omitted.

> Back then people wrote assembly language themselves. Not only this. It made for more compact code, and memory was very expensive. So expensive that 64kB was practically unheard of. In 1980, 4kB would cost $100 or so. If I read it correctly, the original board with the 6800 was shipped with 128B.

>memory was very expensive No lie! I recall paying $200 for a Godbout 12KB (static RAM) board kit (96 1K chips to hand-socket) for my H-8 (8080; Heathkit included no RAM). Later added another 12KB for an incredible 24KB total. Only a few years later at a swap meet I landed two 16KB manufactured boards for only $50!

Brutal times!

A similar thing happened with SGI workstations. Drop $20 on a high end box, score one for a fraction on ebay some while later. Not long enough later.

Re: Motorola 6800

#127

Post by jacquesm »

exmadscientist wrote: post #106
mark-r wrote: post #54

Earlier quoted context omitted.

I think I have a 68HC11 sitting around that I picked up for a project and never used. I wonder if it's worth anything?

One-off hobbiest/repairman/desperation quantities will be available for years. It's industrial, new-build quantities that are going to be problems. And, yes, the 68HC11 was on December's EOL list, so I hope anyone who was using it in products has a plan! (Or hire my company, we fix things like that... not that it's the most fun work in the world, we have other things we'd rather be doing....)

Can't you just use one of these?

https://www.microsemi.com/existing-parts/parts/151966

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