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38

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. ...


25

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

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.


21

I am looking for information on a training language called "WhatDoesItDo". It was called WADUZITDO Well, for training purposes, you might check out the online-version at Waduzitdo.org. It hosts a faithful (*1) port to JavaScript (*2), even including a few quirks of the original 6800 version. It offers as well an online reference of all legal ...


20

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

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

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 ...


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 the ...


13

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.


13

A CP/M implementation can be found in the SIG/M archives, volume 28 as waduzit.com, waduzit.doc and waduzit.pas. From the Pascal source: { +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + PROGRAM TITLE: What Does It Do? + + + + WRITTEN BY: Larry Kheriaty, ...


12

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 ...


10

Shortest coding (I came up so far): Instruction Bytes Cycles TPA 1 2 Transfer P(rocessor status) to (accumulator) A EOR A,#$01 2 2 Invert bit 0 (carry bit) using exclusive OR TAP 1 2 Transfer (accumulator) A back to P(rocessor status) --- --- 4 6 Of course this ...


10

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 ...


9

MC6800 supports 197 opcodes and MC6801 (and MC6803) supports 220 opcodes. So there are 23 new opcodes defined: ABX ($3A) ADDD ($C3, $D3, $E3, $F3) ASLD ($05) BRN ($21) JSR ($9D) LDD ($CC, $DC, $EC, $FC) LSRD ($04) MUL ($3D) PSHX ($3C) PULX ($38) STD ($DD, $ED, $FD) SUBD ($83, $93, $A3, $B3) Since JSR instruction already existed, extending the ...


8

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 ...


8

The following book at archive.org contains several applications notes. Among those you have AN-754 on pp. 21-32.


8

No alignment is necessary. There is no paging of any kind either. Any 16-bit register can be stored to or retrieved from any memory address, odd or even. There is one thing though, if the accessed memory addresses are in the range from $0000 to $00FF, these can be accessed by using direct memory addressing opcodes that only take 8-bit memory address as ...


7

The MacroAssembler AS I use The Macroassembler AS. It's modern, multiplatform (Unix, Windows, DOS) with macros and all that other good stuff, still supported and under development, and supports an amazing variety of CPUs (around 60), including modern MCUs such as Amtel AVR. It's very nice to be able to use the same assembler for all one's 8- and 16-bit ...


7

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...


7

TL;DR: SWTPC and their 6800 system did sell quite well and over a longer time than all of its competition. The question is rather why do most people only know MITS/Altair, which I'd say is rather a hype in hindsight - plus the same effect that made the PC ubiquitous: Cloning. The Long Run When considering 'success' of a single machine or manufacturer it is ...


7

The DAA instruction on 6800 just works on the accumulator based on the data it contains and the flags register as set by the previous instructions. So it does not know what instruction it was and whether it was valid or not in relation to BCD arithmetic, it simply does what is told. An interrupt happening before DAA instruction will not be an issue, as the ...


7

The 6502 works with a single square wave clock signal that is connected to Phi0 pin 37. The chip has a built-in clock generator to use this clock input to internally generate two anti-phase non-overlapping clocks and will output these on two clock output pins, Phi1 (3) and Phi2 (39). The 6800 also needs two anti-phase non-overlapping clocks for internal ...


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

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 ...


5

The one I'm using on Windows is vasm: http://sun.hasenbraten.de/vasm/ vasm is a portable and retargetable assembler to create linkable objects in various formats or absolute code. Multiple CPU-, syntax and output-modules can be selected. Many common directives/pseudo-opcodes are supported (depending on the syntax module) as well as CPU-specific extensions. ...


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

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 ...


5

For the 6800 the same basic considerations as for all other CPUs are valid, as already mentioned in the 8080 answer is as well valid here: Background The question may stem from a mixup between data size requirements and data bus size. Alignment issues can only come up with designs that have a finer address granulation than the external data bus and ...


5

I strongly suspect CP/M was the key. Plenty of 8080 (and by extension, Z80) machines ran other operating systems, particularly the Radio Shack TRS-80 line. But the basics of Altair, Imsai, Osborne, Kaypro, NorthStar and so many others promoted the Intel 8080/compatible market in a huge way. CP/M led to mass-market business software like WordStar, dBase II, ...


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