Questions tagged [6800]

Motorola 6800 family of processors. This does not include the similarly-numbered but different 6809 family.

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21
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12answers
4k views

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

I've just finished reading Charles Petzold's book, Code: The Hidden Language of Computer Hardware and Software. In it Charles explains building relays into gates, gates into logic components, and ...
16
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1answer
1k views

What's the timeline of Motorola 6800-family CPUs from 1974 to 1979?

According to Wikipedia, The Motorola 6800 was released in 1974. Between that and the release of the 6809 in 1979 (or 1978?) there was at least one other 6800-series CPU released, the 6802 ...
15
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2answers
2k views

Looking for information on a programming language called WhatDoesItDo

I am looking for information on a training language called "WhatDoesItDo". It was used in 1978 at Austin Community College on a Motorola 6800 CPU. If anyone has any information, I would ...
13
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6answers
2k views

Was the MC6800 a PDP-11 or PDP-8?

According to Gordon Bell, the 6800 was based on the PDP-11. According to Chuck Peddle, it was a PDP-8. Can anyone with knowledge of the PDP's pass judgement?
12
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1answer
208 views

What are the added opcodes for MC6801/MC6803?

What new opcodes were added to Motorola MC6801/MC6803? Background for the question, and what I've figured out so far (correct me if I'm wrong): The Motorola MC6801 (and MC6803) had an "enhanced ...
11
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1answer
286 views

Inverting the carry flag on an M6800

Are there any tricks that can be used to invert the carry flag on the 6800, in as few bytes as possible? This is the shortest subroutine I've come up with, which is straight forward: INVC: BCS ...
8
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0answers
212 views

Behavior of lesser known illegal M6800 opcodes

The M6800 had a few illegal opcodes, including the (in)famous HCF (Halt and Catch Fire). The following illegal opcodes were revealed in BYTE Magazine, December 1977: $14: NBA $87: STAA immediate $C7: ...
7
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2answers
482 views

How did the 6809 achieve source-code compatibility with the 6800?

The 6809 has 59 instructions, as compared with 78 on the 6800. So far as I can see, the 6809 lacks instructions that the 6800 has, such as aba, eorb and the transfer instructions (tba, tap and the ...
7
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2answers
619 views

What 6800 assembler to use?

Does anyone know of a good, modern Motorola 6800 assembler? I've used dasm, which I quite like (and it's even actively developed), but it doesn't actually support 6800. It supports 6803, which is ...
6
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2answers
310 views

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

Having only a single index register and no addressing mode indexing against 16-bit addresses in memory seems to have been widely considered a primary reason that the Motorola 6800 fared poorly in ...
6
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2answers
831 views

Does the 6800 always handle unaligned access correctly?

I asked a similar question about the Intel 8080 to which I guessed the answer would probably be yes, because later Intel CPUs did fully handle unaligned access. I am less sure about the Motorola 6800, ...
4
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2answers
115 views

6800 I flag at reset

I have written an emulation of the Heathkit ET-3400A microcomputer trainer in Java, mainly to see if I could do it and to get my feet wet in Java. Odd question, but there's a discrepancy (one of many,...
3
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1answer
333 views

What is a more featureful and/or better coded 6800 disassembler for modern machines than f9dasm?

I'm currently using [this version of f9dasm] on Linux to disassemble a moderately large Motorola 6800 program (Altair 680 Basic, about 8 KB in size). f9dasm isn't too bad, but I'd prefer to use ...
2
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2answers
160 views

Why did the SWTPC 6800 Computer System not take off? [closed]

In 1974, a major semiconductor company released its first 8-bit CPU that was good enough to build a serious computer around. In 1975, a smaller company built a computer around it, a horizontal box ...
2
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2answers
188 views

Where can I find the Motorola Application Note AN-754?

Urgently need a copy of Motorola Application Note AN-754 "Device Operation and System Implementation of the Asynchronous Serial Interface Adapter". I have two boards from college days (1979) ...
1
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3answers
174 views

How to code for bidirectional I/O for MC6850 ACIA (680x Assembler)

I need a code listing for 6802 (or 6809) to initialize and set the 6850 ACIA into bidirectional serial I/O mode. I have two vintage boards and need to get the ports working and connected before I can ...
1
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1answer
103 views

Why was the SWTPC 6800 Computer System cheaper than the Altair?

In 1974, Intel released the 8080, which basically was the first microprocessor good enough to build a serious computer around. That led to the Altair 8800 the following year, which was the beginning ...
0
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2answers
167 views

How did the 6800's comparison operations work?

Does anyone have a quick primer to the way the 6800's compare-and-branch instructions worked internally? I'm referring to the instructions like BLS that compared a value in memory to the accumulator. ...
0
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1answer
255 views

How do I examine and use the SWTBUG monitor ROM in the SIMH SWTP6800 simulator?

I'd like to examine (disassemble and memory dump) and run the SWTBUG monitor ROM in the SIMH SWTP6800 emulator, but I seem to be having difficulty getting the devices attached properly, or I'm lost in ...