Alexandre Souza - Listas pu1bzz.listas at
Tue Nov 30 14:56:45 CST 2010

    Tony, you live in the seventies ;oD

> You know as well as I do that the cost of the chip is not the major cost
> for a 1-off (or small run) project like this.

    No, but the sum of all chips maybe are :)

> You might well have Z80s, EPORms, RAMs, etc in the junk box (I certainly
> do), but not the latest microcontroller

    I have many microcontrollers in my junk box, and it doesn't need to be 
the latest.

> You may well feel it's a lot easier to solder up a handful of DIL
> packages on stripboard than a fine-pitch SMD packge that requires you you
> to design a PCB first . This in turn may entail obtianign suitable CAD
> tools, something to run them on, and finding a PCB manufacturer (or
> buying the equipoment to do it at home).


    - There are microcontrollers powerful enough for this task, and they are 
all DIP
    - I can design a PCB at home using free tools (Kicad rulez!)
    - I can make boards good enough for fine pitch SMD at home (see my page, and the equipment is all 
made from junk.

    Maybe it is time for you to update your prototype methods :)

> You may well know the assmbly language for the Z80, and have the
> assembler, etc. Not so fo rthe microcotnroller.

    I know the asm for the Atmel microcontrollers. Also, I have the original 
(and free) assembler from Atmel. BTW, the programmer is also cheap, 5 
resistors on your parallel port can do the task. BTW, there are lots of 
compilers for atmel microcontrollers, and they run on windows, DOS and even 
linux.  Since they are portable, I can do development on my Octane (Irix) or 
in my PA9000. (still OS-Less)

> It's a darn sight easier to debug something when you know what it should
> be doing and can see what it is doing. The former is much easier to
> determine for a Z80 than many modern processors (where the instructions
> are not necesarily executed one at a time in the order you expect). The
> latter is also much easier to do on a system with external program memory
> where you cvan conenct a logic analyser to the ROM address lines.

    In modern processors I can use cheap debug tools (which are CHEAP, look 
for the price of the AVR Dragon which is an excellent USB programmer and 
debugger via 1-wire. Ah, cheaper than my cheap logic analyser). And I can 
use (free) simulators to see the code running on my screen.

> If you want a design to last as long as the classic computer it's
> connected to, I would certainly go with the Z80 + memory solution. Z80s
> are very common. The microcontroller may be common _now_, but whata bout
> next year. There are som many fariants with different memory sizes,
> internal peripherals, etc that several times I've needed to find a
> replacement for something made a few years ago onlky to find that that
> particualr chip is rarere than hen's teeth. Oh, there are 'improved
> versions', but they are not drop-in replacements.

    Tell me a microcontroller that was common yesterday and isn't today. 
Using atmel microcontrollers I NEVER had to find a plug-in replacement, 
because most of them are pin-compatible and EVEN COMPILED CODE compatibles.

> I also feel that this idea of always making everything as cheap as
> possible is a big mistake. It seems to lead to poorly made products with
> all sorts of corners cut. As I have said many times before, I can think
> of plentyy of examples where the cost to do it properly would add perhaps
> \pounds 1.00 od xomponents. Say that translates into \pounds 10.00 by the
> time you've added in all the otehr costs. That increase in selling price
> would not have stopped me buying the product. But when I see how many
> corners havec been cut, I am not goign to be happy, I am not going to buy
> any more products from that company, I am goign to tell my friends to
> look elsewhere too.

    Of course, as fewer devices on board, lesser problems of design, 
manufacture and repair I'll have. I'd prefer to use an internal program 
microcontroller (and I'm not saying a newer microcontroller, I can use an 
8751 if suited to the task) than use lots of external components. is an exercise in simplicity 
and ingenuity. These are ALL common-of-the-shelf components, and the circuit 
is modular, you can recreate it any way you like. A SCSI SDD can be done 
with half the components used in this board and another half created from 
scratch (another microcontroller doing the interfacing with the PIA he 

> If you employ me to desgin soemthing, then you get to specify the sort of
> devices to be used. If you want microcontrollers, or FPGA,s or... then
> fine. But if I am doing it for myself as a hobbyist, then I get to pick
> the devices I like best.

    This is YOUR take. When I create something for hobbists, I pick-up the 
devices and techinics I think common hobbysts will have most ease to use. 
The HP9845 board I redid I had lots of work for doing it single face and 
all-DIP, but it was a way to make it reproductible by every hobbist around. 

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