Harold Hallikainen wrote:

>>Some people sometimes confuse the VAX with the PDP-11, because the VAX was
>>an upgrade of the PDP-11 architecture. Though, to be honest, I still think
>>that the PDP-11 has the cleanest assembly language of any machine I've
>>used.
> 
> 
> 
> I agree! It was amazing how things worked out when you started mixing
> various modes and registers to get immediate addressing, indirect
> addressing, etc. As I recall, the instruction word was always something
> like this:
> 
> Operation - Source Register - Source Mode - Destination Register -
> Destination Mode

Close.
Byte/Op/SReg/Smode/DReg/Dmode
More than you ever wanted to know about PDP 11 architecture.

http://research.microsoft.com/users/GBell/CGB%20Files/New%20Architecture%20PDP11%20SJCC%201970%20c.pdf
Page 672.


> How you mixed those created tha magic.

My favourite was the 'fill memory' instruction.

Mov -(R7),-(R7) ;move predecrement indirect program counter to ...

Placed at top of memory it copied itself down to the bottom
and then caused a halt with bus fault (no memory).

Robert
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