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Questions tagged [homebrew-cpu]

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Is a feedback loop from program counter input to output problematic?

I'm designing a very simple CPU to be built on a custom PCB. I designed the CPU in LogicCircuit, and it seems to work. But I'm wondering it a specific part of the CPU will also work in real life. I ...
RenX's user avatar
  • 143
4 votes
3 answers
2k views

How to do signed 16-bit arithmetic on an 8-bit processor?

For example, to add two 16-bit numbers on my 8 bit machine, I add the low bytes together, then the high bytes together, and then add the carry flag to the high byte of the output. This strategy falls ...
Max Zabarka's user avatar
3 votes
1 answer
141 views

Is there any computing system you can make yourself that you can connect to the internet? [closed]

Is there any computing system, kit or project where you would actually assemble components to form a rudimentary computer which could actually be used to send basic transmissions over the internet? In ...
Julius Hamilton's user avatar
0 votes
2 answers
372 views

What TTL circuit should I use for an SRAM cell

I am trying to build a 16 byte RAM module with only bjt transistors and resistors. And I am looking for a suitable circuit for a memory cell. From what I have understood there are two paths I can take:...
joupy's user avatar
  • 39
1 vote
2 answers
110 views

Should I build my own tri-state buffers? [closed]

I am attempting to build a simple CPU from only BJT transistors. It will have a bus so I will need some tri-state buffers. Can I/should I build them, or should I buy a chip? Is the risk of damaging ...
joupy's user avatar
  • 39
4 votes
1 answer
321 views

How to minimize microcode complexity in 8-bit home-brew CPU

tldr; I built and later extended Ben Eaters 8-bit breadboard computer. After the initial build I integrated 16-bit program counter and memory address registers, redesigned the instruction set and ...
Scott vanVoss's user avatar
2 votes
1 answer
112 views

What's the saturation speed of a transistor and the wires between inside a modern CPU?

I'm tinkering with a specialized CPU design and I'd like to calculate/estimate the saturation time of a circuit that may eventually be part of a CPU made with current technology. For this I need to ...
Mikeologist's user avatar
0 votes
3 answers
557 views

Can you use a cpu without a motherboard?

For instance, could you get a printed circuit board and connect the cpu to that? I want to connect multiple cheap cpus to each other without spending thousands of dollars on a motherboard that will ...
user11937382's user avatar
31 votes
3 answers
10k views

Can you make a CPU out of electronic components drawn by hand on paper?

I explored a lot of literature about paper-based electronics recently, and one particular paper caught my interest: “Handwritten Oxide Electronics on Paper” (DOI: 10.1002/admt.201700009) by Elvira ...
Zoé Martin's user avatar
1 vote
5 answers
580 views

12-bit homebrew computer?

I'm planning my first homebrew computer. I'd like to perform calculations with 8-bit numbers. My op codes will be 4-bit numbers. I'll be building this on breadboards so I'd like to keep things as ...
Peter's user avatar
  • 133
2 votes
1 answer
480 views

Designing an instruction set for a homebrew computer

I'm going to begin the adventure of building an 8-bit homebrew computer. Right now, I'm considering the instruction set. SAP-1 seems a bit too sparse, so I'm designing my own. Some facts: My primary ...
Peter's user avatar
  • 133
3 votes
3 answers
2k views

16-bit Byte-Addressable RAM Interface

I am a beginner to computer engineering and electrical engineering, and I have watched the entirety of Ben Eater's 8 bit breadboard computer series so I decided that because I understood that well, ...
user140052's user avatar
0 votes
1 answer
359 views

What is the maximum length a MC68030 can be placed away from Commodore CDTV motherboard, without affecting timings?

I want to fit a TF536 accelerator card into the Commodore CDTV case, which is a challenge from the perspective of available space. I know there is a relocator board project available, but it still ...
Bartek Malysz's user avatar
0 votes
0 answers
51 views

Is it possible to speculate on the completion of an adder from the first row?

I've seen speculative adders that take an extra clock cycle something on the order of once in 10^5 additions. Often papers on speculative adders claim to need the information from stage 1 and stage <...
John Moser's user avatar
1 vote
0 answers
3k views

Building an Immediate generator for my RISC-V cpu

I'm working on a simulation of a RISC-V CPU (in Logisim-Evolution, not the best, I know). But now, I have almost finished designing it (and so far it works like a charm), and now it is time to build ...
Kralik_011's user avatar
2 votes
0 answers
235 views

FPGA and CPU design: Moving from ideal memory to real RAM blocks

I implemented the single-cycle MIPS design from "Computer Organisation and Design" in Verilog, shown below: I used my own "ideal" data memory implementation, which asynchronously presents the read ...
keksmonster's user avatar
0 votes
1 answer
142 views

Does the 65C02S processor Reset Sequence require that its data pins be connected during reset?

I have a 65C02S processor wired up and the address and data pins connected to an Arduino Mega so that I can print the state of the data bus and address bus for ...
Mario Gianota's user avatar
-1 votes
1 answer
94 views

How to optimise a logic circuit? [closed]

I have the following 15 sets of binary outputs: ...
fadedbee's user avatar
  • 982
2 votes
1 answer
265 views

Designing a Carry lookahead unit using EEPROMs, creates oscillator

I have read something about CLUs (Carry Lookahead Units) and want to build one. I have settled on a design using EEPROMS as ...
Kralik_011's user avatar
4 votes
2 answers
539 views

Approaches to storing and addressing microcode for homebrew CPU

I've been teaching myself about CPU architecture for a while now and have successfully designed a couple myself. They were always based around microcode to drive the CPU's control lines. The microcode ...
Ruud van Falier's user avatar
0 votes
1 answer
2k views

RISC-V: building a datapath for conditional branch instructions

I am simulating a multi-cycle 32bit RISC-V CPU in Logisim Evolution. So far so good. I have implemented almost every instruction from the basic RV32I ISA, but I'm having trouble understanding how the ...
Kralik_011's user avatar
4 votes
1 answer
551 views

Building a byte-addressable memory

I am building a memory module: 32 bits wide, parallel, and, byte-addressable. I did a research and i could not find an memory IC that will suit my needs. It ...
Kralik_011's user avatar
14 votes
3 answers
9k views

FPGA CPUs, how to find the max speed?

I'm just getting into FPGAs, and if I understand correctly, you are connecting logic gates together using code. So if I design a CPU in Verilog, it should connect some logic gates together and work, ...
user avatar
0 votes
1 answer
268 views

Homebrew CPU RAM

I’m trying to build a CPU out of TTL logic chips. I’ve just about got everything finished, however, I’m still working on the RAM. I don’t have any suitable RAM chips I can use, however, I do have a ...
Steve's user avatar
  • 80
1 vote
2 answers
417 views

Power issues on TTL circuit

I am building a homebrew 8-bit computer on breadboards and PCBs with TTL logic ICs (LS, HCT, and ALS families.) This is a small portion of the circuit (3 modules): I'm using an ordinary phone charger ...
André Baptista's user avatar
8 votes
3 answers
2k views

Why are the SRAM data and address pins numbered? [duplicate]

As far as understand, it would make no difference to the operation of an SRAM if you mixed up the order of the address or data pins. E.g. http://www.farnell.com/datasheets/1911297.pdf?_ga=2.220805788....
fadedbee's user avatar
  • 982
1 vote
1 answer
117 views

Electrical properties of a stack of strip board connected by through-hole pins/sockets

I'm aware that breadboards have a limit of 1-2MHz. I think this is because of capacitance. Are there similar limits for a stack of stripboard connected by through-board sockets/pins? Would breaking ...
fadedbee's user avatar
  • 982
1 vote
1 answer
118 views

Would a parallel EEPROM ever output a value that it does not contain?

I understand that when the address input to a parallel EEPROM changes from A to B, the output may show results that aren't the contents of either A or B, for a few nanoseconds. Are these spurious ...
fadedbee's user avatar
  • 982
2 votes
1 answer
751 views

What was the use-case for the 74hc590?

The 74hc590 http://www.ti.com/lit/ds/symlink/sn74hc590a.pdf is a binary counter followed by a register with a tri-state output. I thought about using it in a homebrew CPU design, as it's wider than ...
fadedbee's user avatar
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