A 4$, 4ICs, Z80 homemade computer on breadboard: Z80-MBC (Mobile Breadbord Computer)

Hi all,
I’ve just finished my last crazy useless project (those I like more…):

More info here:

https://hackaday.io/project/19000-a-4-4 … breadboard

Cheers.

Thats twice as much RAM as address space. But I presume thats the smallest RAM you can buy, or perhaps the cheapest.

I quite like the Z80. I prefer it to the 6502.

Only one CPU (Z80) and no ROM!

The MCU Atmega32A “emulates” ROM, I/O for User led and User key, UART with interrupt, clock generator (@4MHz) and reset generator….

Only 4 ICs…

RogerClark wrote:Thats twice as much RAM as address space. But I presume thats the smallest RAM you can buy, or perhaps the cheapest.

I quite like the Z80. I prefer it to the 6502.

Yes the 65c02 is a whopping $2.82… but it’s a rocket ship at 10MHz Knocks spots off the 4MHz Z80
http://www.ebay.com/itm/1pcs-W65C02S8P- … 1988044104
.. but you can go slower.. for less.. ($1.60)
http://www.ebay.com/itm/1PCS-Microproce … OSwZVlXvWq~

ahull wrote:Yes the 65c02 is a whopping $2.82… but it’s a rocket ship at 10MHz Knocks spots off the 4MHz Z80
http://www.ebay.com/itm/1pcs-W65C02S8P- … 1988044104
.. but you can go slower.. for less.. ($1.60)
http://www.ebay.com/itm/1PCS-Microproce … OSwZVlXvWq~

andy

It was years ago I used a Z80.

I recall the Sinclair computers (Z80) vs the BBC (6502), but I don’t recall the BBC being any faster – but perhaps it was.

Z80 needs more clocks per instruction than the 6502 afaik (at least with 8bit instrs).. I’ve spent most of 80ties with Z80 too (and with 68k).
Got an 68B09 recently, but not used yet.
Great usage of mega32 as an ROM and IO! I wonder why not use it at 20MHz and Z80 at 10MHz. A worth of a 20MHz canned oscillator (or a crystal) to add.

RogerClark wrote:I recall the Sinclair computers (Z80) vs the BBC (6502), but I don’t recall the BBC being any faster – but perhaps it was.

Just4Fun wrote:Hi all,
I’ve just finished my last crazy useless project (those I like more…):

More info here:

https://hackaday.io/project/19000-a-4-4 … breadboard

Cheers.

Pito wrote:I wonder why not use it at 20MHz and Z80 at 10MHz. A worth of a 20MHz canned oscillator (or a crystal) to add.

would be away from the “4$, 4ICs” rule…
.. you cannot do it in $4.. the solderless breadboard you are using costs more ..so adding 20cents would not hurt
Great work, I like it

PS: what I am missing today is a good Basic interpreter for the MCUs. In ’83 I got the PC1251 pocket computer/calculator (Z80 based afaik) and since then I cannot find a similar Basic like the one was/is (but written in C)

RogerClark wrote:
I recall the Sinclair computers (Z80) vs the BBC (6502), but I don’t recall the BBC being any faster – but perhaps it was.

There were 128k Spectrums as well I think, but the RAM had to be paged in and out, as its a 8 bit cpu with 16bit addressing, so can only addresss 64k of RAM and ROM.

I dont know how that was handled by the 6502, but it was probably paged as well.

That’s remind me that Apple-III (3 not 2) had 128K also.
Yes, it was also by doing paging, usually 48K base RAM, and the ROM were switched with several banks of 16K of the remaining RAM.

FYI – an 8051 – for example the 33MHz single clock 40pin DIL DS89c450 (or any others probably) – can use up to 16MB of rom/ram via banking the 64k (256x64kB, banking via an 8bit port). Supported automatically by C in Keil and IAR. And it works. The only limitation is an array or a function has to be < 64kB (such it fits inside a bank).
Not sure how the 6502 or the Z80 is supported in C with such tricks today
I got ZX81, ZX Spectrum, Atari 520 but no C was available for it at that time (80ties) as far as I can remember. It could be done in asm too, but lot of effort required

Pito wrote:
I got ZX81, ZX Spectrum, Atari 520 but no C was available for it at that time (80ties) as far as I can remember. It could be done in asm too, but lot of effort required

From what I recall, the Sinclair Z80 based machines, could store assembler in a REM statement in the first line of the BASIC, as it was always in the same position in RAM.

I recall having to enter assembler op code numbers directly in to the keyboard, as I don’t recall there even being something as complex as an assembler (but they may have been some available).

I still remember some of the decimal op code numbers for things like call JMP which was 195 decimal and I recall to load one of the 16 bit registers was op code 33 decimal for load HL I think

z80 NASCOM as in NAScom ASM mebler – yep – cpm on 5.25″ £800 ukp then i modded the fdc circuit to switch clock speed
to the fdc – 8″ was the standard distribution media from CPMUK library group. wrote a program to translate the media as well.
anyone remember skew tables 1,7,13,19 or 1,3,5,8 etc

6502
LDA #55 A9 #immediate value
LDA mem A5 mem addr
LDA ?? A3??? something??
LDA (indirect zeropage), offset y – my all time favourite

stephen
(edit1 minor)

MFM Hard disk G=C800:5 – more of my precious brain cells permanently dedicated to useless facts

Apple ][ : call -151

Hi all,
as “promised” CP/M 2.2 up and running on two “floppy” emulated with two 24LC1025…

Here more info.

Cheers.

Are you planning on selling those as a kit? It takes me back to my green CRT days, writing stuff in complied Microsoft basic.. not ‘cos it was any good, just ‘cos it was all that came with the machine. You could do a lot on a CP/M machine… then I move on to Unix/Xenix and a whole new world opened up.

ahull wrote:Are you planning on selling those as a kit?