8 ms·

Motorola's pioneering 8-bit 6800: Origins and architecture

139 points by klelatti 3y ago

dboreham 3y ago
Nice article. I'd totally forgotten that they launched with a modem chip (6860) in the family. Forward thinking!
- Someone 3y ago
  > Forward thinking! Not really, I think. Doesn’t it directly follow from (FTA)b“Motorola’s 700 page manual for the system even showed how to use the 6800 family to create a complete ‘Point-of-Sale’ terminal”? In the 1970s, how would you connect that to a computer without a modem?
  - kjs3 3y ago
    If it's like the ones I worked with, serial connection to the System 36/38 in the back room.
    - Someone 3y ago
      The System/36 is from 1983. It would have been the System/32, and that cost about $1000 per month, according to Wikipedia. What shops would have a that in the (air-conditioned) back room?
      - kjs3 3y ago
        1) No, when I was involved they were s/36 (on smaller sites) and s/38 (on large and/or central site). The S/38 was from the 70s. They were in the long process of replacing as I recall older System/3 (not 32) retail support machines. 2) $1000 a month is not much money for a retail store large enough to have multiple POS systems, even in 1983 dollars. And you could purchase them if you didn't want to lease. 3) I'm assuming by the 'air conditioning' comment, you're imagining some refrigerator sized minicomputer. You can look at that System/36 Wikipedia page and see pictures of 2 S/36 models that are large deskside cabinets (think of the giant PC AT tower cases of old), are air-cooled, and designed to go in the air-conditioned back room of the store, which all of the stores had.
ezy 3y ago
My first exposure to the innards, from a software perspective, of a computer was a 6809 based system. The first assembly language I learned and the first “real” operating system with multitasking (Microware’s OS-9). I suppose it made an impression— I stuck with Motorola CPUs on my personal computers up to the 68040. :-)
- johngossman 3y ago
  Same. Really nice chip and a really nice OS. Basic09 was way ahead of MSBasic too.
- RaftPeople 3y ago
  Same here for 6809 and OS-9. I remember talking to friends writing 6502 assembly and comparing notes and it made me pretty happy I was working on the 6809 due to various operations and addressing modes.
- gooseyard 3y ago
  I got a 64k CoCo2 when I was 10 or so. The Apple II was the only other computer I had ever used, and so my worldview was that BASIC was how you interacted with a computer. My Radio Shack carried Rainbow magazine and had lots of back issues available, and they were just absolutely delicious to me as a kid with all the program listings and ads for new hardware. What totally confused me at the time though were program listings in assembly (I couldn't figure out how you were meant to type those in) and especially the discussions of OS-9. I didn't know what it was, and even in some cases where I found a Radio Shack with the Tandy OS-9 distro, it was like 100$ and didn't have any games as near as I could tell, so I couldn't figure out why you would pay so much for it. Also I lived in a rural location where even the nearest 6809-oriented BBS would have meant expensive toll calls, so I missed the opportunity to learn that way. Anyway skip forward, I started to college in 1993, immediately found Usenet, then Linux, and spent the next 30 years or so steeped in that world. Every so often I would go back and do a little reading on the 6809 world, but because I had never really understood most of what was going on, I didn't have a great deal of nostalgia. Finally though, a few weeks ago I came across a link (maybe here?) to a release of the VCC emulator, and although I had played with a couple of 6809 emulators before, I hadn't really gone down the rathole of finding the MultiPak roms, or hard disk controller paks, etc. I found a couple of hard drive images, one from the NitrOS9 Ease of Use project, and another random NitrOS9 image packed with old software. What was particularly fascinating to me was the NitrOS9 source itself- since my introduction to Unix was in the 486-MMU-having-era, to see what people were able to do with a 6809 and an assembler was just a joy to read and understand. I feel like probably everything that has ever needed doing on a 6809 has probably been done, and I've done enough 8 bit assembly stuff in school that I don't have a powerful urge to go back and make something myself, but boy what a feeling of having come full circle when I cd'd into the NitrOS9 source directory and found a makefile of all things! I feel so fortunate to have been able to live through a time of such explosive growth and change, and hope to get the chance to do a little OS-9 hacking when I retire some day :)
trzy 3y ago
Why wasn’t this chip more common in arcade and game consoles vs. 6502 and Z80? Cost?
- daltont 3y ago
  Williams Electronics used the 6809 in Defender, Robotron, Joust and Sinistar. It was more expensive. Tandy chose it for the TRS-80 Color Computer and sacrificed dedicated sound generation hardware for it to keep costs down.
  - koz1000 3y ago
    It also ran Williams' line of pinball machines all the way until 1999.
    - csixty4 3y ago
      Same year I faxed them a resume touting my 8-bit assembly experience. Dodged a bullet there, although I'm sure I could have picked up another architecture pretty quickly.
      - koz1000 3y ago
        We switched to C++. Nobody had a problem with the switch, although multitheading became a sticky point with some of the developers so we had to write an API to simulate nonpreemptive tasking like the old assembly system.
  - kjs3 3y ago
    The 6809 is not the same things as the 6800. Related, but quite different.
  - cmrdporcupine 3y ago
    Although the 6809 was assembly-source level compatible with most of the 6800 opcodes, it was not binary compatible, and was in fact a totally new (better) design.
  - 3y ago
julian55 3y ago
I liked the 6800, it was the first microprocessor I used, back in 1975. For programming in assembler I preferred it to the later 6502.
- systems_glitch 3y ago
  The comparison with 6502 is often made, for obvious reasons, but the 6800 is definitely more of a "real processor" feature-wise! The order of magnitude in price difference and radically different intended applications are of course why that is so.
  - dboreham 3y ago
    I don't think the 6800 and 6502 had different intended applications. The 6502 is just a second pass at designing the same product for the same market but with "design for manufacturing" given priority so it was quite a bit cheaper to make.
    - systems_glitch 3y ago
      It is very cut-down compared to other processors of the time. Part of that was cost reduction, but part was also intended applications. I'm struggling to find it now, but I've got a transcript of an interview with I believe Chuck Peddle (may have been Bill Mensch) where they discuss it.
    - systems_glitch 3y ago
      Bill Mensch interview, IEEE Spectrum article: https://spectrum.ieee.org/q-a-with-co-creator-of-the-6502-processor https://spectrum.ieee.org/q-a-with-co-creator-of-the-6502-pr...
  - djmips 3y ago
    How is a 6800 more of a "real processor" feature-wise? They seem pretty similar to me - in fact I seem to recall that the 6501, a sister chip to the 6502 was "pinout" compatible with the 6800. Are you thinking the 6809? Oh I see you are talking about the 16 bit stack pointer and probably the 16 bit Index register. Fair enough on an 16 bit address bus those are fairly convenient but it's interesting that it just tends to mean if you use SOA or AOS for you data design. I don't think 6502 is really much harder to code than 6800 or 6809.
jdporter 3y ago
Back in the day, I did quite a bit of programming, professionally, on 6800-family CPUs, mainly 6850 and kin. It was an absolute pleasure to work with. The 6502, by comparison, felt like an absolute nightmare.
- flopsamjetsam 3y ago
  How would you compare the 6502 to the 6800? I cut my assembly teeth on the 68000 in the Amiga but always heard plenty about the 6502 due to the C64, but would love more perspective on how it compares to other CPUs.
  - jacquesm 3y ago
    Not the OP, but I'll give that a shot since I cut my assembly teeth on both of these, the Z80 and the '09 afterwards (and then back the 6502 because of the BBC Micro). Both are fine processors, the 6502 was technically not quite where the 6800 was but nothing that you couldn't solve using a couple of macros (and a Macro assembler was table stakes for anybody serious enough to go after this stuff and so you rolled your own because buying one was prohibitively expensive). The 6502 had an edge in available software and books, especially once the Commodore took hold. Community mattered, even back then! The 6800 was laid out much more sensible from an instruction set perspective, the term used is 'orthogonality', if you know the rules you can predict the existence of a particular mnemonic and parameters easily, whereas with the 6502 it was mostly a matter of learning it all by heart. Easy to do because both were tiny in comparison with todays CPUs. I suspect that's where the GP's nightmare comment relates to, the fact that the 6502 always felt like it could have been so much better if they had spent a bit more time on this subject. The 6800, it's more modern and upgraded brother, the 6809 and the much larger 68000 all were much more logical and predictable. The Z80 became widespread due to - amongst others - Sinclair with the ZX-80 and ZX-81, and Radio Shack using them in their line of TRS-80 micro computers, and a large number of people cut their teeth on those. I had access to them at work (I worked for Tandy on Saturdays, which was the European name for RS) and never found that chip much to my liking, but it was the engine behind the CP/M software environment. Programming in assembler (or even directly in machine code) is an exercise in abstraction to the point that you have to have a very good memory and to be able to limit the scope of what you are doing to be able to make any progress at all. But it beat the pants of BASIC (the most common alternative on micro computers at the time) in terms of speed and control so if you wanted to do anything serious with those machines that's how you did it. The 6502 had awesome hardware support in terms of peripherals and the machines you found it in (with the BBC Micro model 'B' as the pinnacle of home computing at the time) and the 6800/6809 had an edge if you wanted to roll your own system from scratch. Various bus based systems (S-100, Eurocards, VME) gave you the option to build systems and to swap out the CPU with something else. The BBC again led the way here by speccing a bus called 'the Tube' (a pun on the London underground) that allowed you to build specialist co-processors that used the original BBC as an I/O processor.
kayo_20211030 3y ago
It's an interesting piece, but would it have killed someone to proofread it?
- z500 3y ago
  Yeah I love this blog, but pretty much every post is like this.
  - phendrenad2 3y ago
    Looks fine to me, which makes me wonder if I'm also a bad writer.
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kens 3y ago
The patent for the 6800 chip reveals some interesting features. Most curious is the slush maker shown in the drawing on the first page: https://patentimages.storage.googleapis.com/be/e4/fa/8e78e829202f35/US3987418.pdf https://patentimages.storage.googleapis.com/be/e4/fa/8e78e82... (The patent office messed up and swapped drawings; there's a slush maker patent with a diagram showing instruction decoder, registers, and so forth.)
- djmips 3y ago
  Oh phew, because I was going to need you to explain how this mysterious Slush Storage worked!
- jacquesm 3y ago
  That's hilarious, well spotted!
WalterBright 3y ago
I was baffled by the PDP-10 assembler reference manual. For example, I didn't know what a stack was, what a register was, etc. Eventually, I got a hold of the 6800 instruction set manual. It had what, 40 instructions? Small enough for me to "get" it. All of a sudden, it all made sense. So I have a soft spot for the good ole' 6800! I eventually designed, built, and programmed my own 6800 single board computer. I had a blast with that project.
- rapjr9 3y ago
  If anyone feels like breadboarding a 6800 microcomputer here's some schematics for a very simple one: http://zoom.interoscitor.com/PetersonEnterprises/Consulting/WritingSkills.html http://zoom.interoscitor.com/PetersonEnterprises/Consulting/... It's pretty tedious to program it since the I/O is all in binary and you have to use toggle switches to key in binary machine code.
- fsckboy 3y ago
  i had a similar experience, read the Popular Electronics 8080 article but couldn't understand it. Got my hands on TI 7400 and Intel 8080 databooks and just kept reading them front to back, over and over, till all the little fragments I could glean started to make sense together. Then I wire wrapped an 8080 board of my own design. (well, two of them, the first was a wiring nightmare, didn't work, so I had to start over, but I was much more skilled at that point, and my wiring was clean, and it worked right off the bat) I was most proud of noticing that on the 8080 there is some sort of halt signal pin, and a separate pause signal pin (might not have those names right, maybe it was memory ready?). Anyway, one of them detected the leading edge and the other detected the trailing edge of the clock, so I was able to rig up a pushbutton for single stepping the processor without having to figure out how to make a pushbutton debouncer circuit which I was having a lot of trouble with... good times
  - jacquesm 3y ago
    That was quite the achievement, and - alas - one that you probably couldn't replicate today. How old were you if I may ask?
bell-cot 3y ago
Sadly, it sounds like Motorola's management dysfunction and incompetence at chip manufacturing go back quite a ways.

139 points by klelatti 3y ago

dboreham 3y ago

Nice article. I'd totally forgotten that they launched with a modem chip (6860) in the family. Forward thinking!

Someone 3y ago
> Forward thinking! Not really, I think. Doesn’t it directly follow from (FTA)b“Motorola’s 700 page manual for the system even showed how to use the 6800 family to create a complete ‘Point-of-Sale’ terminal”? In the 1970s, how would you connect that to a computer without a modem?
- kjs3 3y ago
  If it's like the ones I worked with, serial connection to the System 36/38 in the back room.
  - Someone 3y ago
    The System/36 is from 1983. It would have been the System/32, and that cost about $1000 per month, according to Wikipedia. What shops would have a that in the (air-conditioned) back room?
    - kjs3 3y ago
      1) No, when I was involved they were s/36 (on smaller sites) and s/38 (on large and/or central site). The S/38 was from the 70s. They were in the long process of replacing as I recall older System/3 (not 32) retail support machines. 2) $1000 a month is not much money for a retail store large enough to have multiple POS systems, even in 1983 dollars. And you could purchase them if you didn't want to lease. 3) I'm assuming by the 'air conditioning' comment, you're imagining some refrigerator sized minicomputer. You can look at that System/36 Wikipedia page and see pictures of 2 S/36 models that are large deskside cabinets (think of the giant PC AT tower cases of old), are air-cooled, and designed to go in the air-conditioned back room of the store, which all of the stores had.

ezy 3y ago

My first exposure to the innards, from a software perspective, of a computer was a 6809 based system. The first assembly language I learned and the first “real” operating system with multitasking (Microware’s OS-9). I suppose it made an impression— I stuck with Motorola CPUs on my personal computers up to the 68040. :-)

johngossman 3y ago
Same. Really nice chip and a really nice OS. Basic09 was way ahead of MSBasic too.
RaftPeople 3y ago
Same here for 6809 and OS-9. I remember talking to friends writing 6502 assembly and comparing notes and it made me pretty happy I was working on the 6809 due to various operations and addressing modes.
gooseyard 3y ago
I got a 64k CoCo2 when I was 10 or so. The Apple II was the only other computer I had ever used, and so my worldview was that BASIC was how you interacted with a computer. My Radio Shack carried Rainbow magazine and had lots of back issues available, and they were just absolutely delicious to me as a kid with all the program listings and ads for new hardware. What totally confused me at the time though were program listings in assembly (I couldn't figure out how you were meant to type those in) and especially the discussions of OS-9. I didn't know what it was, and even in some cases where I found a Radio Shack with the Tandy OS-9 distro, it was like 100$ and didn't have any games as near as I could tell, so I couldn't figure out why you would pay so much for it. Also I lived in a rural location where even the nearest 6809-oriented BBS would have meant expensive toll calls, so I missed the opportunity to learn that way. Anyway skip forward, I started to college in 1993, immediately found Usenet, then Linux, and spent the next 30 years or so steeped in that world. Every so often I would go back and do a little reading on the 6809 world, but because I had never really understood most of what was going on, I didn't have a great deal of nostalgia. Finally though, a few weeks ago I came across a link (maybe here?) to a release of the VCC emulator, and although I had played with a couple of 6809 emulators before, I hadn't really gone down the rathole of finding the MultiPak roms, or hard disk controller paks, etc. I found a couple of hard drive images, one from the NitrOS9 Ease of Use project, and another random NitrOS9 image packed with old software. What was particularly fascinating to me was the NitrOS9 source itself- since my introduction to Unix was in the 486-MMU-having-era, to see what people were able to do with a 6809 and an assembler was just a joy to read and understand. I feel like probably everything that has ever needed doing on a 6809 has probably been done, and I've done enough 8 bit assembly stuff in school that I don't have a powerful urge to go back and make something myself, but boy what a feeling of having come full circle when I cd'd into the NitrOS9 source directory and found a makefile of all things! I feel so fortunate to have been able to live through a time of such explosive growth and change, and hope to get the chance to do a little OS-9 hacking when I retire some day :)

trzy 3y ago

Why wasn’t this chip more common in arcade and game consoles vs. 6502 and Z80? Cost?

daltont 3y ago
Williams Electronics used the 6809 in Defender, Robotron, Joust and Sinistar. It was more expensive. Tandy chose it for the TRS-80 Color Computer and sacrificed dedicated sound generation hardware for it to keep costs down.
- koz1000 3y ago
  It also ran Williams' line of pinball machines all the way until 1999.
  - csixty4 3y ago
    Same year I faxed them a resume touting my 8-bit assembly experience. Dodged a bullet there, although I'm sure I could have picked up another architecture pretty quickly.
    - koz1000 3y ago
      We switched to C++. Nobody had a problem with the switch, although multitheading became a sticky point with some of the developers so we had to write an API to simulate nonpreemptive tasking like the old assembly system.
- kjs3 3y ago
  The 6809 is not the same things as the 6800. Related, but quite different.
- cmrdporcupine 3y ago
  Although the 6809 was assembly-source level compatible with most of the 6800 opcodes, it was not binary compatible, and was in fact a totally new (better) design.
- 3y ago

julian55 3y ago

I liked the 6800, it was the first microprocessor I used, back in 1975. For programming in assembler I preferred it to the later 6502.

systems_glitch 3y ago
The comparison with 6502 is often made, for obvious reasons, but the 6800 is definitely more of a "real processor" feature-wise! The order of magnitude in price difference and radically different intended applications are of course why that is so.
- dboreham 3y ago
  I don't think the 6800 and 6502 had different intended applications. The 6502 is just a second pass at designing the same product for the same market but with "design for manufacturing" given priority so it was quite a bit cheaper to make.
  - systems_glitch 3y ago
    It is very cut-down compared to other processors of the time. Part of that was cost reduction, but part was also intended applications. I'm struggling to find it now, but I've got a transcript of an interview with I believe Chuck Peddle (may have been Bill Mensch) where they discuss it.
  - systems_glitch 3y ago
    Bill Mensch interview, IEEE Spectrum article: https://spectrum.ieee.org/q-a-with-co-creator-of-the-6502-processor https://spectrum.ieee.org/q-a-with-co-creator-of-the-6502-pr...
- djmips 3y ago
  How is a 6800 more of a "real processor" feature-wise? They seem pretty similar to me - in fact I seem to recall that the 6501, a sister chip to the 6502 was "pinout" compatible with the 6800. Are you thinking the 6809? Oh I see you are talking about the 16 bit stack pointer and probably the 16 bit Index register. Fair enough on an 16 bit address bus those are fairly convenient but it's interesting that it just tends to mean if you use SOA or AOS for you data design. I don't think 6502 is really much harder to code than 6800 or 6809.

jdporter 3y ago

Back in the day, I did quite a bit of programming, professionally, on 6800-family CPUs, mainly 6850 and kin. It was an absolute pleasure to work with. The 6502, by comparison, felt like an absolute nightmare.

flopsamjetsam 3y ago
How would you compare the 6502 to the 6800? I cut my assembly teeth on the 68000 in the Amiga but always heard plenty about the 6502 due to the C64, but would love more perspective on how it compares to other CPUs.
- jacquesm 3y ago
  Not the OP, but I'll give that a shot since I cut my assembly teeth on both of these, the Z80 and the '09 afterwards (and then back the 6502 because of the BBC Micro). Both are fine processors, the 6502 was technically not quite where the 6800 was but nothing that you couldn't solve using a couple of macros (and a Macro assembler was table stakes for anybody serious enough to go after this stuff and so you rolled your own because buying one was prohibitively expensive). The 6502 had an edge in available software and books, especially once the Commodore took hold. Community mattered, even back then! The 6800 was laid out much more sensible from an instruction set perspective, the term used is 'orthogonality', if you know the rules you can predict the existence of a particular mnemonic and parameters easily, whereas with the 6502 it was mostly a matter of learning it all by heart. Easy to do because both were tiny in comparison with todays CPUs. I suspect that's where the GP's nightmare comment relates to, the fact that the 6502 always felt like it could have been so much better if they had spent a bit more time on this subject. The 6800, it's more modern and upgraded brother, the 6809 and the much larger 68000 all were much more logical and predictable. The Z80 became widespread due to - amongst others - Sinclair with the ZX-80 and ZX-81, and Radio Shack using them in their line of TRS-80 micro computers, and a large number of people cut their teeth on those. I had access to them at work (I worked for Tandy on Saturdays, which was the European name for RS) and never found that chip much to my liking, but it was the engine behind the CP/M software environment. Programming in assembler (or even directly in machine code) is an exercise in abstraction to the point that you have to have a very good memory and to be able to limit the scope of what you are doing to be able to make any progress at all. But it beat the pants of BASIC (the most common alternative on micro computers at the time) in terms of speed and control so if you wanted to do anything serious with those machines that's how you did it. The 6502 had awesome hardware support in terms of peripherals and the machines you found it in (with the BBC Micro model 'B' as the pinnacle of home computing at the time) and the 6800/6809 had an edge if you wanted to roll your own system from scratch. Various bus based systems (S-100, Eurocards, VME) gave you the option to build systems and to swap out the CPU with something else. The BBC again led the way here by speccing a bus called 'the Tube' (a pun on the London underground) that allowed you to build specialist co-processors that used the original BBC as an I/O processor.

kayo_20211030 3y ago

It's an interesting piece, but would it have killed someone to proofread it?

z500 3y ago
Yeah I love this blog, but pretty much every post is like this.
- phendrenad2 3y ago
  Looks fine to me, which makes me wonder if I'm also a bad writer.
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kens 3y ago

The patent for the 6800 chip reveals some interesting features. Most curious is the slush maker shown in the drawing on the first page: https://patentimages.storage.googleapis.com/be/e4/fa/8e78e829202f35/US3987418.pdf https://patentimages.storage.googleapis.com/be/e4/fa/8e78e82... (The patent office messed up and swapped drawings; there's a slush maker patent with a diagram showing instruction decoder, registers, and so forth.)

djmips 3y ago
Oh phew, because I was going to need you to explain how this mysterious Slush Storage worked!
jacquesm 3y ago
That's hilarious, well spotted!

WalterBright 3y ago

I was baffled by the PDP-10 assembler reference manual. For example, I didn't know what a stack was, what a register was, etc. Eventually, I got a hold of the 6800 instruction set manual. It had what, 40 instructions? Small enough for me to "get" it. All of a sudden, it all made sense. So I have a soft spot for the good ole' 6800! I eventually designed, built, and programmed my own 6800 single board computer. I had a blast with that project.

rapjr9 3y ago
If anyone feels like breadboarding a 6800 microcomputer here's some schematics for a very simple one: http://zoom.interoscitor.com/PetersonEnterprises/Consulting/WritingSkills.html http://zoom.interoscitor.com/PetersonEnterprises/Consulting/... It's pretty tedious to program it since the I/O is all in binary and you have to use toggle switches to key in binary machine code.
fsckboy 3y ago
i had a similar experience, read the Popular Electronics 8080 article but couldn't understand it. Got my hands on TI 7400 and Intel 8080 databooks and just kept reading them front to back, over and over, till all the little fragments I could glean started to make sense together. Then I wire wrapped an 8080 board of my own design. (well, two of them, the first was a wiring nightmare, didn't work, so I had to start over, but I was much more skilled at that point, and my wiring was clean, and it worked right off the bat) I was most proud of noticing that on the 8080 there is some sort of halt signal pin, and a separate pause signal pin (might not have those names right, maybe it was memory ready?). Anyway, one of them detected the leading edge and the other detected the trailing edge of the clock, so I was able to rig up a pushbutton for single stepping the processor without having to figure out how to make a pushbutton debouncer circuit which I was having a lot of trouble with... good times
- jacquesm 3y ago
  That was quite the achievement, and - alas - one that you probably couldn't replicate today. How old were you if I may ask?

bell-cot 3y ago

Sadly, it sounds like Motorola's management dysfunction and incompetence at chip manufacturing go back quite a ways.