intro

who is peepaw?

Me!

why a retro computer?

help a kid understand computers

why z80?

cheap, available, cheap

the plan

build from scratch

build something like a tec1

https://en.wikipedia.org/wiki/TEC-1

a great guide is the 1981 book build your own z80 computer

Build

Your Own Z80 Computer Steve Ciarcia/

get started with nop tester

http://www.z80.info/z80test0.htm

want an expandable system

keep the cost down

work up to a system like the jupiter ace (which is like a zx-81

sinclair computer)

https://en.wikipedia.org/wiki/Jupiter_Ace

getting started, the nop test

use an arduino mega board and some forth to spin up the most basic

z80 system

https://gitlab.com/8bitforce/retroshield-hw/-/tree/master/hardware

give the z80 5 volts, a clock and the right data and it will happily

start up and run through its address space doing nothing

the nop tester, in software

make a forth logic probe

https://en.wikipedia.org/wiki/Logic_probe

use a gate method of frequency counting

https://ww1.microchip.com/downloads/en/Appnotes/doc8365.pdf

create a few forth words to make a "logic probe" and test that

probe

https://pajacobs-ghub.github.io/flashforth/ff5-tutorial-guide.html#_counting_button_presses

need an arduino mega running flashforth

https://store.arduino.cc/products/arduino-mega-2560-rev3

https://flashforth.com/atmega.html

datasheet

https://store.arduino.cc/products/arduino-mega-2560-rev3

https://ww1.microchip.com/downloads/en/devicedoc/atmel-2549-8-bit-avr-microcontroller-atmega640-1280-1281-2560-2561_datasheet.pdf

some jumper wires

z80

solderless bread board

the code walk through, start from the bottom up note: ( -- ) are

stack effect comments, back slashes are plain comments

constants

variable

@ ! mset mclr mtst

set up external interrupt, int4, arduino board pin4

the source code

declare some constants and variable as labels

variable Compare

variable Count

$100 constant PINH these labels come from the atmega2560 datasheet

$101 constant DDRH

$102 constant PORTH

$a0 constant TCCR4A

$a1 constant TCCR4B

$a8 constant OCR4A

$2c constant PINE

$2d constant DDRE

$2e constant PORTE

$6a constant EICRB

$3d constant EIMSK

: ext4.irq ( -- ) Count @ 1+ Count ! ;i the frequency counter

: logicprobe-init ( -- )

1249 Compare ! 100 hz

%0000.1000 DDRH mset h3 output

%0100.0000 TCCR4A c! toggle d6, ph3 on compare match

0000.1011 %TCCR4B c! set ctc mode, clk/64

Compare @ OCR4A ! set compare value

%0 DDRE c! e input

0001.0000 PORTE mset pullup on e4

%0000.0010 %EIC