PDP-11 architecture

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The PDP-11 is a 16-bit minicomputer designed by DEC.

Addressing modes

Mode Name Symbolic Description
0 Register R (R) is the operand
1 Register deferred (R) (R) contains address of operand
2 Auto-increment (R)+ (R) is the address; (R) is incremented by 1 or 2, in case of byte or word instructions.
3 Auto-increment deferred @(R)+ (R) is the address of the address; (R) is incremented by 2
4 Auto-decrement (R)- (R) is decremented by 1 or 2, in case of byte or word instructions; R is address.
5 Auto-decrement deferred @(R)- (R) is decremented by two; (R) is the address of the address.
6 Index X(R) (R) + X is the address.
7 Index deferred @X(R) (R) + X is the address of the address