myke,

On the following points, I agree.  Make that a minority of two.

Since we are programming all parts to date serially and in-system, I have
not addressed some of the programming issues you mention.

Doug

> ----------
> From:         myke predko[SMTP:myke@PASSPORT.CA]
> Sent:         Wednesday, July 08, 1998 10:01 AM
> Subject:      Re: ATMEL
>
>
> The AVR is really designed for code development for High-Level Languages
> and
> such is probably the best 8 bit processor architecture I've seen for it
> (again, for the full AVR, not the bastardized 1200).  The three 16 bit
> index
> registers really gives you superior control over data structures.
>
> A nice feature of the AVR over the PIC is the use of separate interrupt
> source vectors (rather than the PIC's one) which follows the 8051 lead.
> And, following this lead, some interrupts will have their hardware reset
> just by executing the return from interrupt instruction.
>
> The "true" AVR (not the 1200) has an instruction pointer stack that you
> can
> access including a "push" and "pop" instruction.  With this, you can
> implement funky things like RTOSes (which you can't in the PIC).
>
> NOT EVERY instruction executes in one instruction (clock) cycle;
> Instructions can take 1, 2 or 3 cycles.  As well, the instruction set is
> best described as "quirky"; not all registers can be addressed in
> different
> instructions or different instructions can take different lengths of time
> depending on the instruction that follows.
>
> The one instruction per clock cycle is something I can take or leave
> (having
> grown up with 8051s and 8088s I'm used to converting clock cycles to
> instruction cycles to actual timings); I find a much more significant
> issue
> comparing the PIC to the AVR is the different instruction timing; I find
> the
> PIC much easier to time applications and this also leads to the next
> point:
>
> Where the AVR archictecture falls short of the PIC is in the area of
> register I/O (both I/O pin registers and other "SFR").  The AVR is
> designed
> with three memory spaces (GPR, SFR and SRAM).  While *some* of the GPRs
> are
> bit addressable, none of the Special Function Registers ("SFR"), which
> contain the Status Register, Interrupt control, and I/O functions, are
> which
> means they have to be loaded into the GPR space, manipulated and then
> written back.  Coupled with the different instruction timing, a PIC
> running
> at the same speed as an AVR will definitely be able to do Parallel/Bit I/O
> faster than an AVR.
>
> The PIC really is the superior part if you're going to be programming in
> assembly language.  I found that I could dispense with the instruction
> data
> sheet very quickly as I was developing applications (especially critically
> timed ones).  This is not true for the AVR.
>
> In terms of which is better; EPROM/EEPROM(Flash)/ROM, I've come to the
> conclusion that this is not a deciding factor in what is the best MCU.
> Now,
> for developing applications, I obviously want to have an EEPROM/Flash MCU,
> but when I have something going out to customers, I want the cheapest
> device
> possible and you can talk to Atmel that says Flash is best because you can
> update your field population, Microchip that says EPROM is best because
> you'll never update the parts in the field can customize the part on the
> manufacturing line rather than have to buy a large number of ROMed parts
> and
> Motorola (and others) that says ROM is best because it's always cheapest.
> Pick which is best for you.
>
> I was really disappointed in the AVR simulator and Assembler (especially
> compared to MPLAB); it does allow you to input data (ie buttons or
> Stimulus
> Files).  They really don't measure up to the Microchip products in term of
> features.  I found the Assembler to quite feature poor as well compared to
> MPASM (although this may change in the future).
>
> I've voiced these concerns before (on Kalle's Atmel list) and told that
> I'm
> in a minority of one, but here they are for what they're worth.
>
> myke
>
> This week in myke's Book Room: "Point of Honor" by Maurice Medland.
>
> http://www.myke.com/Book_Room
>