Since you apparently believe you've found some self-contradictions, perhaps
you'd like to point them out. I'll be happy to explain my meaning, since I
certainly haven't changed my thinking on this matter.
The fact remains that while the Apple along with nearly any other platform is
quite capable of helping one learn about computing, it's pretty limited where
learning about microPROCESSORs and their application is concerned. Dogging the
Apple, which, admittedly, I never learned to like, won't shed light on what will
really be helpful as far as teaching folks about the application of
microPROCESSORs, and dogging the Apple isn't what I set out to do. I simply
wanted to point out that, while the Apple does support plug-in cards, it has a
number of limitations resulting from the compromises involved in integrating the
processor with the video timing and I/O scheme that was selected.
A device that would probably be more educational is the Motorola MC6801L1, which
is a 6801 with the Lilbug monitor in ROM, or a Motorola MC68701-1 programmed
with the LILBUG monitor (available for free on their MCU web site). This device
has a number of configurable "modes" in which it can be used, ranging from
"single-chip" mode to a full-blown microprocessor mode, and several in-between
modes. With the 6801L1 you have the Lilbug debug monitor which has a
mini-assembler built into it. There's very little external hardware needed to
make this thing work, and anyone interested in microprocessors as anything other
than a personal computer/video toy, would have little difficulty hooking up the
necessary oscillator, switches, and serial port buffers to make it into a simple
development/evaluation tool. Since it's capable of producing a set of parallel
ports, or of producing a full 16-bit address bus and 8-bit data bus with the aid
of an external address latch, it offers the user an opportunity to fiddle with
the timing, decoding logic, etc, as he sees fit. Use of the monitor, however,
requires that one choose one of three baud rates, provided by the firmware. The
device, however, is capable of a wide range of baud rates, etc. It is really a
very impressive device, contemporary with the 68000 and 6809, but targeted at a
different market. There's also a ROMless version, the 6803, which is often
found on old ST-412-style hard disk drives. Miniscribe, CMI, and others used
the 6803, and RMS and others used the 68701, which is the EPROM version.
Hitachi made a compatible set of devices, though their EPROM parts used a
piggy-back EPROM.
The 805x family is another set of processors that offer some interesting
possibilities, including a built-in serial port, and the 803x types are the
ROMless versions of them. These are still widely available today, most notably
in EEPROM/FLASH versions from ATMEL and others. There are a lots of free
development tools, e.g. assemblers and a few compilers, for the 805x family and
a few resident debug monitors. Dallas Semiconductor makes a RAM-based version
of the chip that allows it to be used as an in-circuit development tool, among
other things, and Intel, among MANY others made an 875x series, which used
EPROM. These things have been around for nearly 20 years and their popularity
hasn't seemed to wane much. They are, like the 6801 series, capable of
functioning either as a single-chip device or as an expanded microprocessor with
a 16-bit address bus and an 8-bit data bus. These were also used on a wide
range of HDD's likely to be lying in the back of the closet.
I'd say either of those devices, available during the Apple era, would give more
support to one wishing to experiment and learn about the use of microPROCESSORs
than does the Apple, or any other desktop platform. The reality simply is that
involvement of the processor in a platform like the Apple, with its video and
I/O features, is necessarily limiting, hence interferes with learning about the
features which are most critical to microPROCESSOR application, e.g. timing,
decoding, and other low-level features of that ilk.
Dick
----- Original Message -----
From: "Sellam Ismail" <foo_at_siconic.com>
To: <classiccmp_at_classiccmp.org>
Sent: Saturday, July 14, 2001 9:25 AM
Subject: Re: Apple II for intro to microprocessors
> On Sat, 14 Jul 2001, Richard Erlacher wrote:
>
> > As in that infamous previous thread, it seems some people have chosen
> > to read what they wanted to read rather than was was written. That's
> > not my fault, though.
>
> In defense of those who have good reading and comprehension skills, it
> should be noted that some people have trouble expressing their thoughts in
> a clear and concise manner, and sometimes even contradickt themselves.
>
>
> Sellam Ismail Vintage Computer Festival
> ------------------------------------------------------------------------------
> International Man of Intrigue and Danger http://www.vintage.org
>
>
Received on Sat Jul 14 2001 - 13:35:12 BST