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Questions tagged [8080]

For questions about the Intel 8080 8-bit microprocessor

3
votes
3answers
260 views

Did the original Intel peripherals use latches as input registers?

This is more a question to satisfy my curiosity. When looking at the original timing diagrams for reading and writing (e.g. for the 8255 and the 8250), these signals are never expressed in function ...
1
vote
1answer
273 views

What is the difference between an 8080 and an 8051? [closed]

What are the features of the Intel 8051 architecture that allow it to successfully act as a microcontroller? Hypothetically can the general-purpose 8-bit architecture like Intel 8080 do everything the ...
5
votes
4answers
226 views

What stops an IO device from driving the databus longer than the CPU expects?

For example, consider the case of handling an INT interrupt signal in the Z80. When the CPU makes the IORQ signal active, it expects the requesting IO device to place a vector onto on the databus. And ...
2
votes
1answer
163 views

Source code of front-panel entered Altair 8800 programs

I'm looking for the source code of short programs for the MITS Altair 8800 (let's say < 50 instructions to make the question more specific), so they can be entered by using only the front panel. ...
2
votes
3answers
606 views

How can a Z80/8080/6502 use VGA?

I've come across a couple of projects that manage to get VGA working with the Z80 and similar CPUs: Veronica (6502 CPU, VGA signal generation by AVR) ZC160 (Z80 CPU, VGA signal generation by GAL) c-...
1
vote
4answers
288 views

Intel 8080 and Altair 8800. 256 I/0 ports, but only 7 free RST (interrupt subroutine) - how it works?

I have looked this video - Altair 8800 - Interrupt Acknowledge Cycle and have few questions (I have read wikipedia Intel 8080 article, Altair 8800 Operator's manual, Charles Petzold "Code" and few ...
26
votes
4answers
8k views

How did 8 bit processors perform 16 bit arithmetic?

How did 8 bit processors such as the Z80 and 8080 perform 16 bit arithmetic? They have an 8 bit data bus, so how does the ALU perform 16 bit arithmetic on the register pairs? Z80 architecture diagram ...
15
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2answers
1k views

The start of x86: Intel 8080 vs Intel 8086?

Why is it said that all modern Intel processors of the x86 family are said to descent from the Intel 8086 and not the Intel 8080? From the Wikipedia article on the Intel 8086, The 8086 gave rise to ...
8
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3answers
736 views

Intel 8080 - Behaviour of the carry bit when comparing a value with 0

I'm in the process of writing an emulator for the Intel 8080. The description of the CMP instruction from Intel's 8080 programming manual (see page 20) says the following: The specified byte is ...
10
votes
1answer
265 views

Why was the 8080's JumP immediate instruction placed where it was?

On the 8080 there are many instructions with parallel forms. Three of these are CALL, RET and JP, which all have conditional and immediate forms. Note: I am using Z80 terminology because that is what ...
0
votes
1answer
280 views

Why did this Hitachi 6301 assembler routine only work once?

I am trying to learn assembler on the various retro machines I own, or am about to buy. Today I tried converting this 8080 routine (which worked, repeatedly): | START: | MVI A,0 | 8000 | 3e | | ...
3
votes
1answer
303 views

Carry flag in 8080/8085 subtraction

How is the carry flag set during a subtraction by the 8080 or 8085 processor? For addition, the carry flag is set if the result is greater than 255 (i.e. if it overflows). From the programmer's ...
16
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4answers
3k views

What's the difference between “opcode” and “instruction” in this Zilog ad?

In a Zilog ad from 1976 comparing the Z80 and Intel 8080, the following table is presented: What is the difference here between "Instructions" and "OP Codes"? In my experience, the two terms are ...
5
votes
1answer
535 views

How was the Microsoft PDP-10 8080 emulator developed? [closed]

Altair BASIC, the first version of Microsoft BASIC, was developed using an Intel 8008 emulator, modified to emulate an Intel 8080, running on a PDP-10 computer. This emulator was originally designed ...
22
votes
1answer
2k views

What is the relative code density of 8-bit microprocessors?

When RAM is at a premium, as it was in the old days, a greater code density of an instruction set can be a substantial advantage. (Click saver: Code density refers loosely to how many microprocessor ...
16
votes
3answers
1k views

DIY Project using 1970s 8-bit CPU, is it possible?

I've recently really wanted to try and design a computer system around a retro 8-bit CPU such as the Zilog Z80 or the Intel 8080, and I would appreciate some sanity checks! I was inspired by Ben Eater'...
6
votes
0answers
102 views

Manual for DIAGNOSTICS II V1.2 - CPU TEST SUPERSOFT ASSOCIATES

I am building a 8080 emulator. I found some useful test suites here. The emulator passes the first test suite (8080/8085 CPU Diagnostic, version 1.0, by Microcosm Associates), but not the second ( ...
12
votes
1answer
212 views

What is the difference between i8080 and i8080a?

There is some info over the net regarding 'some i8080 bugs were fixed in i8080a', but the exact bugs and differences are not usually disclosed. So, what is the exact difference between i8080 and ...
15
votes
8answers
2k 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 ...
19
votes
3answers
2k views

Why did Pokémon Red have so many overflow bugs?

(This question also applies to other Game Boy games, but Pokémon seems to be one of the best-documented.) Pokémon Red & Blue (Red & Green in Japan) is a pair of Game Boy games about capturing ...
36
votes
2answers
5k views

How did the Z80 instruction set differ from the 8080?

The Zilog Z80 microprocessor, known for its use in the ZX Spectrum, was designed to be a backwards-compatible extension to the Intel 8080 processor. It introduced several new instructions to the 8080'...
6
votes
1answer
289 views

What exactly were those 808X computers that would switch to 80386 upon Ctrl-Alt-Del?

A while ago I've been told that some generic-brand PC, (yet packed on an IBM5150 case) had the ability to become a 80386 upon pressing Ctrl-Alt-Del (warm reboot) ? I guess there might have been (for ...
5
votes
3answers
945 views

LCD Displays with the Intel 8080

A colleague of mine mentioned that in college he wrote a slot machine program on an Intel 8080 using an LCD display. What kind of display communication protocol existed on the Intel 8080? How was ...
11
votes
1answer
366 views

8080/8085 Instruction Test Suite

(This question was inspired by Comprehensive test suites for MOS 6520 PIA / 6522 VIA / 6526 CIA) Is there a comprehensive test suite for the Intel 808X series of processors? Something that would ...
8
votes
0answers
440 views

What are the technical differences between the Midway 8080 and Taito 8080 hardware boards?

In my research on 1970s-era arcade machines, I've noticed that both Midway and Taito created games which used Intel's 8080 microprocessor. However, each company had their own host boards which ...
15
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2answers
2k views

What was the first arcade game to use a microprocessor instead of discrete logic?

Many authors credit Space Invaders as the first blockbuster game to have been written with an onboard microprocessor (Taito used Intel's 8080 for game logic), but there is also references to Taito's ...
8
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2answers
605 views

Intel 8080 Read/Set Interrupt Mask Instructions

According to Intel's 8080-8085 Assembly Language Programming guide, the OP Code 20 corresponds to the Read Interrupt Mask (RIM) instruction, and 30 corresponds to the Set Interrupt Mask (SIM) ...