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).
:oO
- 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,
http://tabalabs.com.br/eletronica/tts/index.htm) 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.
http://micha.freeshell.org/ramdisk/index.php 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
created.
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.