On 1/12/2019 4:45 PM, allison via cctalk wrote:
The 6809 (hitachi 63B09) are about as close to PDP11 in general
structure and
instruction set and could boogy. The were a cusp 16 bitter (not really
but close).
The 8088/86 was not wonderful, and what came after had all the side baggage
to not help. At that time I was voting for 68000 to win!
So was I, but all we got was the MAC (128K memory) and game machines.
Allison
I am building a TTL computer from 1973 as I said earlier. This is to
compiete
with the PDP 11 and the PDP 8. Major design features a single memory bus
and character I/O (10 bits) and word/character addressing.
The hardest part is getting a card edge connector for the bus, in .156 inch
pitch. All I can find are 28/56 and 36/72 pin connectors. A possible
design is loosely based of the 6800 cpu but 18 bits. EBAY for the hard
to find parts and the rest off the shelf TTL or LS part depending the
bus clock. Since proms seem to out in 1973 I will be using them.
876 543 210 987 654 321
+-----------------------+
|ooo|baa|xx-|±##|###|###| normal opcode
+-----------------------+
+-----------------------+
|ooo|I00|###|###|###|##0| bcc opcode + 1K words
+-----------------------+
+-----------------------+
|00h|000|00-|000|000|000| hlt opcode
+-----------------------+
+-----------------------+
|000|000|xx.|±##|###|###| lea opcode
+-----------------------+
ooo opcode b byte aa jmp,ac,ix,sp xx #,Z,ix,sp
A simpler 20 bit cpu is possible but might be to
primitive a design with only word addressing
and possible random logic design having NO proms
in the design.
+-----------------------+
|ooobaa|xx####|####|####| normal opcode
+-----------------------+
It is really amazing how fast electronics changed between
1971 and 1976.
Ben.
