20 Nov
2009
20 Nov
'09
6:47 p.m.
Chuck Guzis wrote:
On 20 Nov 2009 at 8:16, Al Kossow wrote:
The Osborne book lists 9 variants:
65x2 x=0|1
65x3
65x4
65x5
6506
varying in clock pins, interrupt pins, number of address-bus pins, and on-board
ROM. I didn't know about this until I ran across it while reading the Osborne
book, and then started noticing when I'd run across some of the small 28-pin
variants on occasion.
I believe this would be the first u-proc to take this approach of creating a
family by paring down a 'standard', that the PIC family and other u-controllers
would later leverage.
Chuck Peddle told me a couple of months ago that
the 6502 was never
intended to be a general-purpose microprocessor, it was designed to be
a replacement for hard-wired logic. They had a die size target to hit
to get to the price point they wanted and pulled out things they
thought were unnecessary for its use in that market. In particular,
the length of the registers. I had always wondered why they built a
microprocessor with an 8 bit stack pointer, when the previous 6800
design had 16.
There were variants of the 6502 with mask-programmed ROM on board (I
have a Micropolis floppy drive with one) and 3M Iomat quarter-inch
tape drives had a controller that's not much bigger than a file card
that holds a 6502, EPROM, a little SRAM and a VIA. So the thing
*was* suited to what we'd call microcontroller use.