[HN Gopher] Motorola's pioneering 8-bit 6800: Origins and archit...
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Motorola's pioneering 8-bit 6800: Origins and architecture
Author : klelatti
Score : 61 points
Date : 2023-12-12 18:53 UTC (4 hours ago)
(HTM) web link (thechipletter.substack.com)
(TXT) w3m dump (thechipletter.substack.com)
| dboreham wrote:
| Nice article. I'd totally forgotten that they launched with a
| modem chip (6860) in the family. Forward thinking!
| Someone wrote:
| > 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 wrote:
| If it's like the ones I worked with, serial connection to the
| System 36/38 in the back room.
| ezy wrote:
| 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 wrote:
| Same. Really nice chip and a really nice OS. Basic09 was way
| ahead of MSBasic too.
| RaftPeople wrote:
| 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 wrote:
| 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 wrote:
| Why wasn't this chip more common in arcade and game consoles vs.
| 6502 and Z80? Cost?
| duskwuff wrote:
| Primarily cost. In 1975, the 6800 cost $175 (which was already
| a dramatic reduction from the initial price of $360); the 6502
| launched that year at $25.
|
| Motorola dropped prices on the 6800 in response, but they still
| couldn't match MOS's pricing.
| systems_glitch wrote:
| Indeed, the mask correction process that MOS came up with was
| really their killer advancement w.r.t. keeping design cost
| down, even considering the dramatically simpler 6502 core.
| daltont wrote:
| 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 wrote:
| It also ran Williams' line of pinball machines all the way
| until 1999.
| csixty4 wrote:
| 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.
| kjs3 wrote:
| The 6809 is not the same things as the 6800. Related, but
| quite different.
| cmrdporcupine wrote:
| 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.
| angiosperm wrote:
| The 6502 was a better chip (designed with hindsight on the
| 6800), and also cheaper. Z80 could run 8080 code.
| kjs3 wrote:
| Just because it came second, doesn't mean it's better. It was
| cheaper, and you can see where they cut corners to be
| cheaper. For me, if _nothing else_ , the 16-bit stack and
| index registers in the 6800 make it hands down a better chip
| to program. But the 6502 was cheaper, sure, and some people
| probably like to spend all day thinking about what stuff to
| cram into the first 256 bytes to be performant.
| systems_glitch wrote:
| If I had to pick one over the other to write serious
| software in forever, it'd definitely be the 6800.
|
| Remember, you can also spend all day exploiting zero page
| mode in the 6800, but you'll never be able to move the
| 6502's stack :P
| angiosperm wrote:
| The "zero-page", the low 256 bytes, amounted to a big
| register bank; compilers for 6502 used it that way. The
| hardware stack was for return addresses only, and was
| plenty; a zero-page pair pointed to the stack for arguments
| and locals. The designer of the ARM noted that her programs
| ran faster on 6502 than when ported to early 8086, largely
| because the latter was relatively so inefficient.
| jhallenworld wrote:
| For me, 6502 was annoying because of its:
|
| - Incomplete set of branches
|
| - Indexed Indirect mode (z-page,x) is un-orthogonal and
| rarely used, better to have indirect indexed with x, just
| as it has with y: (z-page),x
|
| - Difficult to deal with data more than 256 bytes in
| length.
|
| The big problem with the 6800 is only on index register.
| Fixed with 6809 and 68HC11.
| systems_glitch wrote:
| Remember that the 6502 and its related chipset was not
| designed to compete with the 8080 or 6800 for general
| computer applications, but rather with the Intel 4004 for
| cheap, low-parts-count embedded applications! Keeping that in
| mind, a lot of the 6502 design decisions make a lot more
| sense.
|
| That folks turned out complex, feature-complete operating
| systems several times on 6502 is as impressive as those
| things being done on e.g. the DEC PDP-8, IMO. Doubly so when
| you consider that the 6502 hackers were often just that,
| hackers and hobbyists without an industrial-grade budget.
| dboreham wrote:
| The Z80 was a generation later, so its appropriate comparison
| is the 6809, used in the Dragon and Tandy Color Computer.
| julian55 wrote:
| 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 wrote:
| 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 wrote:
| 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.
| jdporter wrote:
| 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.
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(page generated 2023-12-12 23:00 UTC)