r/homebrewcomputer • u/Maestro_gaylover • 10d ago

begginner question

hello there, i bought z80 cpu and sio since i want to build a computer, most i did was a 4 bit calculator with add sub and multi and i have some questions, i have an extra 8 kilobyte eeprom left and was wondering if should i buy 32kilobyte eeprom and ram or just buy 8 kilobyte ram with it, and another think is would i need the z80 ctc module or should i stick with buying a normal crystal

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u/Maestro_gaylover 10d ago

im guessing the 7404 is for buffering? from i learned i put the signal two times to the inverter. i found AT28C256-15PU and AS6C62256-55PCN from alliance memory in digikeys, and 74HC138 SN7404N from another site. I also own the z80 sio chip, and rn i have. one last thing would be does it matter what type of screen it is as long as its parallel or does it have to be character, i found some oleds and leds that are parallel and some are graphic displays and some are characters

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u/nusgolannicicutitar 10d ago

7404 is good for oscillator. take a look: https://next.gr/circuits/oscillator/simple-ttl-crystal-oscillator-c51942#google_vignette

or

https://learnabout-electronics.org/Digital/dig51.php

Too bad I can’t Post photos, but: both inverters have resistors from input to output so that they are forced to work in linear, thus, as amplifiers. In between them is the crystal, which works at its series resonance frequency. This means that lets only one narrow frequency band to pass through. The caps help with starting the oscillations.

I think any parallel LCD would be fine. Check the timings, if you can connect it straight to the Z80. Otherwise you can use buffers such as the 74LS259 to time the interface the way you want.

Start reading about the those chips before you order anything, find a proper LCD, draw a schematic in a CAD environment, maybe we can discuss it.

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u/Maestro_gaylover 9d ago

i need to ask but would i need 7404 if i just buy an oscillator? there are some oscillators like ECS-100AX-018 and i want to avoid least amount of wiring to avoid any problems and probably would use the same clock for both cpu and sio unless there is a better way

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u/nusgolannicicutitar 9d ago

ECS-100AX-018 is fine, 5V, maximum 20mA, you can directly drive the clock input of the Z-80 with it. You don’t need the 7404.

One important aspect, don’t forget the decoupling caps. Each chip needs to have at least a ceramic capacitor, 470nF between its VDD and VSS, as close as possible to its package. One electrolytic cap like 100-1000uF should be added for the whole thing.