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24

Figure 1-1 (page 1-4) in [mot81] gives an overview of the early days of the 6800 family: This can't be read for exact dates so I've included everything that is not clearly after the 6809 and added further details from other sources documented below. Production Annnounced Product 1974-11 1974-03 6800 microprocessor 1976-07? ? ...


24

It was very common to build CPUs out of TTL logic prior to the 4004, 8080 and the 6800. This was the standard way to build later minicomputers. Examples are the Data General NOVA, Xerox Alto and TI-990. Also, if a company needed a processor for, say, a CNC machine or a video game (Vectorbeam), it wasn't unusual for them to build a unique processor from TTL. ...


18

Hmm, an interesting question to be sure. It certainly would have been possible to make something like a 4004 style microprocessor from TTL chips. In fact, when Intel made their microprocessor, the first in the world, they chose not to pursue a patent for it, because they felt that there was no invention there; it was obvious for someone to go and combine the ...


17

Here is an homebrew / educational computer made of LSI / MSI chips : http://www.kenbak-1.net/index.htm Designed in 1971 256 bytes of memory made of MOS shift registers.


14

The Xerox Alto A 1972 machine, officially introduced in March 1973. It had multi-chip CPU built around the 74181 IC. The 74181 represents an evolutionary step between the CPUs of the 1960s, which were constructed using discrete logic gates, and today's single-chip CPUs or microprocessors. - Wikipedia The Xerox Alto had a mouse-driven GUI (yep, a real ...


14

In spirit it's both, thus eventually neither. Features of the 6800 can be put in line with many CPUs of that time - from PDP-8 and -11 all the way to TI's 990 or even IBM's /360 - but none will put it decisively into being based on either. In fact, many of the arguments that can be used to put the 6800 into PDP-8/-11 heritage can as well be applied to the ...


13

Most sources say it was based on PDP-11. Here are citations from the book "Early Home Computers", summarizing the similarities and the differences: Unlike the PDP-11, 6502 and 8080, the 6800 was big-endian, as was the IBM 360 (...) Unlike the PDP-11 and 6502, but like the 8080, the 6800 used borrow carry (...) Unlike the 8080 and especially ...


12

68HC11 should be opcode compatible and it has extra index register. But using the other index register requires an extra prefix byte to indicate non-default register.


11

So far as I can see, the 6809 lacks instructions that the 6800 has, such as aba, eorb ABA becomes PSHS B; ADDA ,S+ - a nifty use of the autoincrement feature. It shows as well were the temporary byte location comes from. After all, stack relative addressing, as well as indexing was one of the main features of the 6809. In fact, looking at his changes it ...


9

There was also the EDUC-8 (pronounced "educate"). It was Australia's first hobby computer, published as a series of articles in Electronics Australia from August 1974 to August 1975. The computer uses 100 discrete logic integrated circuits. There are 98 74 TTL series or 9000 series TTL chips, and two 1Kx1 static RAM chips. The computer runs at 500 kHz, with ...


9

It would have been cost and space-prohibitive to try to build a microcomputer using TTL logic chips, but minicomputers and mainframes were routinely built from such chips (or related technologies like DTL, ECL, etc.). Processors like the 4004, 8008, 8080 and 6800 were not powerful enough for minicomputer and mainframe workloads, so they used simpler (and ...


6

The German hobby-electronics magazine "ELEKTOR" had a project called "Computer 74", named both because of the year of publishing and the TTL logic chip family that made up most of the design. Sorry, I don't remember more about it...


6

The 74181 ALU was available in 1970, so hobbyists could build something with it -- it was $16.50 in quantities of 100. http://apollo181.wixsite.com/apollo181/about Here's a 4-bit computer built around the 74181 and TTL logic: http://jaromir.xf.cz/fourbit/fourbit.html That "thing" doesn't have to be a full CPU though. For example, Midway's 1975 arcade game ...


5

Well, there was an obscure computer called the VAX 11/780 built out of TTL. This was of course not a hobbyist computer, but it doesn't seem to be ruled out by the wording of your question - it was certainly built by 'engineers'. On the amateur front, here's a 1975 newsletter from the (UK) Amateur Computer Club, containing details of a machine called the ...


5

Like many other machines, the 6800 has a compare instruction CMP that compares the accumulator with another operand, specified just as it is in other instructions like ADD and SUB. The CMP instruction, like ADD and SUB, sets the four condition code bits NZVC according to the arithmetic result -- in fact, it is identical with a SUB instruction, except that ...


5

I wonder if there isn't a minor mistake in the CPU being discussed in one of those. It's very easy to see the 68K as nearly a direct descendant of the PDP-11. The 68K has separate data and address registers, but programming it is mostly quite similar to programming a PDP-11. I'd say the 6800 is (much) closer to a PDP-8. If memory serves, the 6800 has two ...


4

The main problem I found with having only one index register on the 6800 was having to constantly load and save source and destination addresses when doing a memory copy (though you could use SP as extra 'index' register so long as interrupts were disabled). Another thing that didn't help was that many instructions took longer than they could have. The ...


3

Perq computers, which were built first in Pittsburgh, PA, and then later, somewhere in England, had a CPU that was mostly built from 74LS parts. "Mostly," because it had one LSI chip, an Am2910 microsequencer. The first Perqs were shipped in 1980--well after the Apple][ and other microprocessor-based computers had hit the market. In fact, the Perq's I/O ...


2

I had largely same requirements for similar CPU but ended up using f9dasm. But if you are serious then look at IDA Pro.


1

I guess that it automated the process of doing an internal LDA,SBC,BNE sort of thing, but that would seem to require an additional internal register for holding the value during comparison? A common way to implement this kind of operation (used on 6502, Z80, at least the early PDP-11s), is to have the ALU compute the subtraction, and then discard the result....


1

As someone who developed on PDP-8 and PDP-11 computers and managed an effort on a 6800, I will say that the 6800 is neither. Furthermore, the PDP-8 and PDP-11 are very different architectures, and their assembler is quite different. An example of a machine which is similar to the PDP-8 is the HP-2100, even though it is 16 bits, the instructions are much ...


1

I say the 6800 is not like a PDP-11 in any useful way. It does not have general registers and it does not have addressing modes as a separate construction from the registers used by the mode. For example, the PDP-11 'indexed' mode is X(Rn), for n = 0 to 7; the case of n = 7 (the PC) gets you PC-relative addressing. By contrast the 6800 has only 1 register ...


1

In overall feel, the MC6800 is clearly more like a PDP-11 than a PDP-8. Word vs. Byte Architecture Like many machines of the 1950s and '60s, from the IBM 701 to DEC's PDP-10, the PDP-8 was a word-oriented machine. Addresses pointed only to full words, loads and stores were always of a full word¹, and every instruction was exactly one word in size, with any ...


1

And to all the other fine answers above, let me add the RCA COSMOS, later better known as the RCA 1802. This was a relatively advanced CPU in 8-bit terms, with 16 16-bit registers (!!) but an 8-bit ALU and instruction set. A number of people, notably Tom Pittman (Tiny BASIC) claimed it to be their favorite CPU design and noted that it had very tight code, ...


1

Memory may not have been quite so much of an issue as people were making it out to be. Keep in mind that the base version of the Altair 8800 (kit price $439) shipped with a "1024 word" (by which they mean byte) memory board populated with only 256 bytes of RAM. If you were willing to work with less, and in particular design your computer to use RAM more ...


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