Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [z80]

The Zilog Z80 is an 8-bit microprocessor designed by Zilog. It powers the popular ZX Spectrum computer.

The Zilog Z80 is an 8-bit microprocessor designed by Zilog and sold from July 1976 onwards. It was widely used both in desktop and embedded computer designs as well as for military purposes. The Z80 and its derivatives and clones make up one of the most commonly used CPU families of all time, and, along with the MOS Technology 6502 family, dominated the 8-bit microcomputer market from the late 1970s to the mid-1980s.

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How do I build a computer with a Z80 microprocessor?

I've got the chip, so how would I add: a clock, RAM, hard drive (maybe EEPROM?), a screen (LCD graphical screen?), input method (keyboard, mouse) ?
user8210
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SRAM isn't blank on powerup, is this normal?

I had finally finished my Z80 memory board, but I was disappointed to see that it wasn't working properly (simple NOP test with the address lines connected to some LEDs) as the counter quickly spiraled out of control instead of incrementing as it…
KeatonB
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Why am I Seeing A Weird "Notch" on the Data Line For Some Logical 1s?

I'm attempting to build a Z80 homebrew computer for some retrocomputing fun and to teach myself the basis of electronic design. For proof-of-concept, I've already assembled a basic system on breadboards successfully in the previous weeks. The…
比尔盖子
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Confused about IN/OUT architecture of z80 chip

I am reading the manual, and it's a bit complex. I can't understand the machine code encoding for the life of me, but that's not my main concern ... my main concern is the address/data buses. I do not understand the difference between the "address…
user33553
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Why is the RESET pin set up like this in this Z80 schematic?

I've found the following schematic: Which after a lot of datasheet reading I mostly understand. The main thing I don't understand, however, is what's going on with the RESET pin. First of all, I understand that the RESET pin is active-low. In this…
Jacob Garby
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Measure square waves without oscilloscope?

I have a Z80 which is misbehaving and want to check the signals. However I do not own an oscilloscope, so I'm looking for another way of checking the square waves on the pins. I basically just need to determine if it is outputting any sign of life,…
Eric
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Can I connect TTL gates directly to the address bus of a Z80 CPU?

I need to know when the 14 MSB bits from the address bus of a z80 CPU are high. To do so my first idea is to use 4 74LS08 ICs (TTL AND gates) reading those lines but I don't know the maximum amount of current that can be drained from the CPU. The…
NeonMan
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How can z80 uses a 4-bit ALU and return results in a single clock cycle?

According to Ken Sheriff's blog post Z80 ALU is 4-bits wide. If we take a look at page 8 and 9 of Z80 User Guide we will find the following information: Clock states T3 and T4 of a fetch cycle are used to refresh dynamic memories. The CPU uses this…
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What components are needed for a 20MHz square wave clock?

I would like to create a 20Mhz clock that generates a square wave for the home-brew Z80 computer I' making. I already have several 20MHz crystal oscillators but am at a loss when it comes to circuit diagrams and other components needed. I have…
VivaDaylight3
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Why do these resistors decouple the two databuses?

The ZX Spectrum is a computer with a Z80 accessing ROM and two separate areas of RAM, one of which is also accessed by a ULA which generates video. If the Z80 wants to access the video RAM, it may be slowed down to fit in with the timing imposed by…
Lorraine
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Z80 Simple Computer Troubleshooting: IORQ pin not going low

I'm following the instructions at http://www.reocities.com/SiliconValley/2072/z80proj1.htm to build a "proof of concept" Z80-based computer. I have wired everything on my breadboard, and programmed the EEPROM with the following program (first…
Nester
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Video Controller Design

I'm designing my own computer based on the Zilog Z80. It has 256KiB of static RAM with paging as well as a few megabytes of flash memory. Everything is going along pretty well until * BAM * I hit a dead end. The problem that I am having is designing…
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Logic family for 3.3 V microcontroller interface

I need to generate a bunch of chip selects for a SPI bus that I want to use on a project. I will use a 36 position (similar to PCIExpress = cheap) card edge connector and etc. The bus is simple : Pin 01 -> Clock Pin 02 -> MOSI Pin 03 -> MISO Pin 04…
Jorge Aldo
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How was the Zero Flag implemented on Z80 ALU?

Z80 was a popular 8-bit processor with a 4-bit ALU. Implementing a zero flag for a register should be straight forward, it would be a logical NOR of all the bits on the register. Something like that would work for a small number of inputs. As for…
GabrielOshiro
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How do I know if I fried my Z80?

I'm working on a free-running circuit like the one here: http://www.z80.info/z80test0.htm The only differences are that I'm using a 4049 clock circuit with a 1 uf cap, and I've added an extra LED at Address pin #3. The resistors call for 470 ohm,…
OrangeCalx01
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