4 Jan
2009
4 Jan
'09
10:40 a.m.
Chuck writes:
I work with both PICs and AVRs (my current project
uses an
ATMega128), but both instruction sets seem to me to be more than a
bit contrived. The AVR less so than the PIC, but still on the "odd"
side of the ledger.
Try programming an 1802 for a while. You'll know you're really into
it when it seems "contrived" that all those other processors can
only use a single of their registers as a program counter :-).
Twisting my mind to switch to 1802 mode and back is a interesting
experience.
The smaller PIC's make perfect sense once you realize they're
Harvard architecture. Bigger PIC's, I never really grokked.
I'm not a 430 evangelist (and suspect that it will
never enjoy the
popularity of the PIC or AVR, which is a shame). I'll work with any
instruction set, but I know what I'd prefer to use.
It's curious that the MSP430's instruction set is close to the GI
CP1600, where the PIC is descended from the very different 1650.
To me it's perfectly obvious that the MSP430 is PDP-11 like, and
in some ways even more orthogonal than the -11. The CP1600 was
substantially less orthogonal, more Nova-like with some
of the registers obviously intended for index use.
Tim.
4 Jan
4 Jan
10:53 a.m.
SNIP_________________________
To me it's perfectly obvious that the MSP430 is
PDP-11 like, and
in some ways even more orthogonal than the -11. The CP1600 was
substantially less orthogonal, more Nova-like with some
of the registers obviously intended for index use.
Actually its much more TMS9900 like than PDP11 like (addressing modes,
machine code layout, number of registers)
not surprisingly since its from TI
Tim.
Peter Wallace
Mesa Electronics
(\__/)
(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination.
11:19 a.m.
On 4 Jan 2009 at 10:53, Peter C. Wallace wrote:
Actually its much more TMS9900 like than PDP11 like
(addressing modes,
machine code layout, number of registers)
not surprisingly since its from TI
You know, you're right-- what the MPS430 lacks is a workspace
pointer. At least interrupts push the status register on the stack,
unlike some other uCs.
Cheers,
Chuck
10:59 a.m.
One must have affection for any proc with instruction "GHI".
An 1802 prob also still somewhat in control of the Earthmade-machine
most distant from Earth.
Steve
Tim Shoppa wrote:
Chuck writes:
I work with both PICs and AVRs (my current
project uses an
ATMega128), but both instruction sets seem to me to be more than a
bit contrived. The AVR less so than the PIC, but still on the "odd"
side of the ledger.
Try programming an 1802 for a while. You'll know you're really into
it when it seems "contrived" that all those other processors can
only use a single of their registers as a program counter :-).
Twisting my mind to switch to 1802 mode and back is a interesting
experience.
The smaller PIC's make perfect sense once you realize they're
Harvard architecture. Bigger PIC's, I never really grokked.
I'm not a 430 evangelist (and suspect that it
will never enjoy the
popularity of the PIC or AVR, which is a shame). I'll work with any
instruction set, but I know what I'd prefer to use.
It's curious that the MSP430's instruction set is close to the GI
CP1600, where the PIC is descended from the very different 1650.
To me it's perfectly obvious that the MSP430 is PDP-11 like, and
in some ways even more orthogonal than the -11. The CP1600 was
substantially less orthogonal, more Nova-like with some
of the registers obviously intended for index use.
Tim.
11:57 a.m.
On 4 Jan 2009 at 13:40, Tim Shoppa wrote:
Try programming an 1802 for a while. You'll know you're really into
it when it seems "contrived" that all those
other processors can
only use a single of their registers as a program counter :-).
Twisting my mind to switch to 1802 mode and back is a interesting
experience.
Well, at least the PC on the 430 is a regular register, operable by
any applicable instruction of the set. Doing a decimal add to the PC
must certainly yield interesting results!
I'd always considered the 1802 to be in a unique position in the
70's, in that it was a (comparatively) low-power CMOS design. No
doubt this was aided somewhat by its simple architecture. Was 1802
RCA's one and only veture in the microprocessor world?
The smaller PIC's make perfect sense once you
realize they're
Harvard architecture. Bigger PIC's, I never really grokked.
The Harvard architecture really falls down in uCs because of lack of
space to store read-only constants. Small PICs have to resort to all
sorts of oddball tricks to accommodate this for things such as lookup
tables. (Use a "return from subroutine with immediate value"
instruction). Upper PICs include instructions to access program
memory and AFAIK, all AVRs have them. Which doesn't make them
strictly Harvard architecture anymore. Had the ROM area included a
space in data memory for constant storage, it might have done the
trick. Yes, there's EEPROM, but it has a different purpose and is
not easy to use.
The 430 drops the charade and adopts a Von Neumann architecture,
relying on the read-only nature of ROM to enforce the separation
between code and data.
To me it's perfectly obvious that the MSP430 is
PDP-11 like, and
in some ways even more orthogonal than the -11. The CP1600 was
substantially less orthogonal, more Nova-like with some
of the registers obviously intended for index use.
How many Nova programmers would have killed for 16 registers? To me,
what distinguishes the CP1600 was its inefficient use of instruction
memory (Yes, I know about the 10-bit ROM, but still...)
Cheers,
Chuck
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