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Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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-...
Ken Shirriff's user avatar
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How common was programming in C targeting 8-bit processors in 1983?

How often was C used to program firmware for 8-bit processors in the early 80s? It would have been a rather unusual choice in 1983. True, C was slowly creeping in, but only on 'big' machines and 16 ...
Raffzahn's user avatar
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27 votes
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What's the timeline of Motorola 6800-family CPUs from 1974 to 1979?

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 ...
cjs's user avatar
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Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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.
Grabul's user avatar
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22 votes

Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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 ...
PkP's user avatar
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21 votes

Looking for information on a programming language called WhatDoesItDo

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 ...
Raffzahn's user avatar
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How did the 6809 achieve source-code compatibility with the 6800?

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 ...
Raffzahn's user avatar
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18 votes

Is there a common name for this 'switch' like 6800 assembly routine?

The term that comes to mind is "dispatch table". This is a table containing pointers to functions, one of which will be chosen based on an index that has been provided or gets calculated. ...
Walter Mitty's user avatar
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17 votes

Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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 ...
Klaws's user avatar
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17 votes

Was the MC6800 based on the PDP-11 or PDP-8?

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 ...
Raffzahn's user avatar
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Was the MC6800 based on the PDP-11 or PDP-8?

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 ...
Martin Maly's user avatar
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Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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 ...
Alan Laughton's user avatar
14 votes

Are there any CPUs or MCUs object-compatible with the 6800 that have additional index registers or addressing modes?

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.
Justme's user avatar
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14 votes

How common was programming in C targeting 8-bit processors in 1983?

I was programming full-time on Aztec-C (for Z-80s) starting in mid to late 1982. Our target systems were embedded devices using STD-Bus. We used CP/M as a dev environment. The company also had ...
Flydog57's user avatar
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What are the added opcodes for MC6801/MC6803?

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, $...
Justme's user avatar
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13 votes

Looking for information on a programming language called WhatDoesItDo

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: { +++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + ...
john_e's user avatar
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12 votes

Does this 1978 code for a 6800 really clear ALL of memory?

Assuming the address space of the CPU is 100% writeable (i.e. no ROM somewhere), these routines seem in fact to clear all of the memory (including the routines themselves) to either zero or the opcode ...
tofro's user avatar
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11 votes

Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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 ...
Ken Gober's user avatar
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10 votes
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Inverting the carry flag on an M6800

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) ...
Raffzahn's user avatar
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9 votes

Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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 ...
dave's user avatar
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What 6800 assembler to use?

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 ...
cjs's user avatar
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8 votes

Was the MC6800 based on the PDP-11 or PDP-8?

I was taking the EE Computer Organization class at UT Austin a few years after the MC6800 came out. We had a guest speaker one day, a local consultant who had been a Motorola employee and who had ...
John R. Strohm's user avatar
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Where can I find the Motorola Application Note AN-754?

The following book at archive.org contains several applications notes. Among those you have AN-754 on pp. 21-32.
UncleBod's user avatar
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Does the 6800 always handle unaligned access correctly?

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 ...
Justme's user avatar
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8 votes
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Why did the SWTPC 6800 Computer System not take off?

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 ...
Raffzahn's user avatar
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8 votes

What does the DAA instruction do?

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 ...
Justme's user avatar
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8 votes
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What were the modifications on the Apple 1 board that would have made it 6800 compatible?

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-...
Justme's user avatar
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8 votes

Is there a common name for this 'switch' like 6800 assembly routine?

Is there a common name for this 'switch' like 6800 assembly routine? No. There is no specific name for exactly this technique. In fact, even generic names vary depending on whom to ask. I do need to ...
Raffzahn's user avatar
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7 votes

Were people building CPUs out of TTL logic prior to the 4004, 8080 and the 6800?

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 ...
Ralf Kleberhoff's user avatar

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