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3 messages
3 total messages Started by Gareths Downstairs Computer Sun, 25 Mar 2018 11:33
The 1802 microprocessor
#621639
Author: Gareths Downstairs Computer
Date: Sun, 25 Mar 2018 11:33
14 lines
2075 bytes
Insofar as it is a radiation hardened device and can
withstand the hostile environment of outer space does not
imply that it is a well thought out instruction set
architecture.

ISTR that it is doubly equipped with both conditional
skip and conditional branch instructions, possibly showing
that the designer had (limited) software experience of the
PDP8 but that indicates that the eye was taken off the ball
for the more essential operations of moving data and performing
arithmetic and logical operations on it, and, especially,
making subroutine calls!

YMMV, it is 40 years this year since dabbling with one.
Re: The 1802 microprocessor
#621650
Author: d... Dennis Boone
Date: Sun, 25 Mar 2018 17:22
12 lines
2146 bytes
 > ISTR that it is doubly equipped with both conditional
 > skip and conditional branch instructions, possibly showing
 > that the designer had (limited) software experience of the
 > PDP8 but that indicates that the eye was taken off the ball
 > for the more essential operations of moving data and performing
 > arithmetic and logical operations on it, and, especially,
 > making subroutine calls!

The 1802 is certainly a bit quirky.  OTOH, it's very efficient in
code size.  SCRT is also odd, but it's not hard, and it's well defined.

De
Re: The 1802 microprocessor
#621646
Author: timcaf...
Date: Mon, 26 Mar 2018 17:27
28 lines
2579 bytes
On Sunday, March 25, 2018 at 7:33:55 AM UTC-4, Gareth's Downstairs Computer wrote:
> Insofar as it is a radiation hardened device and can
> withstand the hostile environment of outer space does not
> imply that it is a well thought out instruction set
> architecture.
> 
> ISTR that it is doubly equipped with both conditional
> skip and conditional branch instructions, possibly showing
> that the designer had (limited) software experience of the
> PDP8 but that indicates that the eye was taken off the ball
> for the more essential operations of moving data and performing
> arithmetic and logical operations on it, and, especially,
> making subroutine calls!
> 
> YMMV, it is 40 years this year since dabbling with one.

While the 1802 was not a traditional architecture, I was 
fascinated by it.  Wrote a bunch of little programs for it.
It seemed like the thing to do was implement Forth on it, 
and then use that :).  It wasn't fast, but it used, AFAICT,
a 1 bit ALU.  I remember being at a trade show and the
demo used a lemon to power the system; very low power.
You could slow down the clock to DC if you needed to.

Ironically, considering your post, there was a CMOS PDP-8
chip (the Intersil 6100) available at the same time.

       - Tim
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