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Re: Newbie: Which MCU/kit to Start?
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This is not the case.

In the 8 bit area the C is not that portable compared to 32 bit
architectures.  8051 has HW BIT addressable memory.

Within the 8051 family the core code is fully portable, usually even
when compiled. Which is more than can be said for PIC's.

The other thing is that there are not always comparable compilers for
all architectures.  There are a wide choice of 51 tools to suit most
kinds of development.


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Neither PIC or AVR are "broad range". Several 8051 vendors, Atmel,
Philips and Infineon for example each have 8051 ranges that are larger
than either PIC or AVR.  More to the point there are often several
popular designs that are implemented by more than one vendor.

If you need more power then there is the 251 (binary compatible) 16 bit
version of the 8051 and the Philips XA.

If Part A is out of stock then part B will have the same core and same
basic peripheral set. Maybe you might have to redo the module
interfacing to a particular peripheral but a lot of the code will not
even need to be recompiled.  

I have seen a project to move from two different 8051's to a third
combining the first two programs. A lot of the code on the new system is
the same code, literally, from the first two projects. the conversion
was very rapid as all the team new the architecture and the tools.

However with the PIC you need a completely new tool chain when moving
from one member of the family to another.

With AVR if they discontinue a part all your tools become redundant and
you need new ones the new architecture. If you can get a full set of
decent tools.

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Not so: Many 8051 are pin compatible and several vendors offer
replacement parts and not just for the basic 8051/2 There are even
Philips LPC parts that can pin replace PIC's :-)

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This is true.. however the speed of redesign when swapping one 8051 type
for another in a CAD package is not difficult. Especially as many of the
pins will be the same and the peripherals (A/D, CAN, Serial, USB, etc)
will have the same external characteristics.  They use standard packages
as well. Then most of the code will be the same.

I spend a lot of my time with 8051 users who have no problem swapping
between 8051 types and vendors.




/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\
\/\/\/\/\ Chris Hills  Staffs  England    /\/\/\/\/\
/\/\/ snipped-for-privacy@phaedsys.org       www.phaedsys.org \/\/
\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/\/

Re: Newbie: Which MCU/kit to Start?

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Is this statement including ASICs and other parts that can't feasibly
be bought in small volumes, though? I based my comment on an
examination of standard parts from Winbond, Atmel and Maxim (Dallas).
It seemed to me that the range of available parts was very fragmented.
If you look at the entire market, there's a smooth spectrum of parts
to match any possible application. If you look at one particular
vendor, there are big notches in the spectrum, and it's not
necessarily easy to move between vendors (certainly not drop-in).

Hence my basic assertion, which was that '51 is a great choice when
you have a reasonably well-specified project, but if you simply have a
need to learn "an MCU family" in order to undertake numerous disparate
projects, it's easier and cheaper (much cheaper) to pick a family with
a relatively broad range of devices, all offered from a single source
with some notes on porting amongst those parts, rather than having to
keep tabs on multiple vendors.

Basically, that narrowed the list down to PIC, MSP430 and AVR. Further
analysis, including devtool cost and the specific requirements of the
family of projects I was discussing, further narrowed me down to AVR
(although either of the other two would have done the job perfectly
adequately).

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Okay, the range of standard products is larger than just the basic
8051, but if you take any specific 51-cored MCU, I think the odds are
against you finding an *exact* replacement from another vendor.
*Something* will be different - peripherals, I/O voltage tolerance,
type/size of code memory, flash algorithms, ... And almost doesn't
count in this case.

Re: Newbie: Which MCU/kit to Start?
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 Porting a single "algorithm" I would agree, but porting
a whole application accumulates the effort.
 Personally, I have not seen much cross-core porting actually
done in embedded systems. Where cores have been changed, it
is normally done at a product-cycle-step.

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 AVR's are not actually that broad, plus most of the first generation
are now tagged 'not for new designs', or pruned.
 In any given package, there are not many code-options - plenty
of cases where a ceiling was hit, and a re-design was needed.
Sure, SW porting to the physically larger sibling was
relatively easy, but the HW impact was significant.

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 A chapter comparing the 'code knees' of AVR, C51 and eZ8 cores
would be interesting.
 Code Knee is where a particular opcode limit kicks in, and  
slower, bulkier code is needed for Data access above that limit.

 Thus eZ8 and 8051 have direct memory opcodes (reach 256 Bytes),
and DJNZ opcodes.
Register frame pointers exist on both 8051 (2 bits) and z8 (8 bits)
- good for fast interrupt context switching.
 80C51 features atomic boolean opcodes, and a large 128 byte SFR
space.
 Index registers on AVR are 16 bit, so more opcodes can
access > 256 bytes, but they do have to be (re)loaded.
( ..etc.. you get the general idea :)

-jg

Re: Newbie: Which MCU/kit to Start?
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You know, I didn't even think of eZ8. Hmm.

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Well... I didn't go into that detailed a level of analysis, since it's
not the primary thrust of the book. But it strikes me that someone has
probably already written a white paper on this topic.

Re: Newbie: Which MCU/kit to Start?
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When is your book ready Lewin, sounds like a nice present to some friends in
competing companies :-)


--
Best Regards,
Ulf Samuelsson   ulf@a-t-m-e-l.com
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Re: Newbie: Which MCU/kit to Start?
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;) My manuscript deadline is 5/31/04 but I am running a little ahead
of schedule (fx: beating head on wooden plank), so I'm hoping it will
be on the shelves towards the start of Q3.

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