PDP-11 Architecture - CPU Registers

CPU Registers

PDP-11 registers
15 14 13 12 11 10 09 08 07 06 05 04 03 02 01 00 (bit position)
Main registers
R0 Register 0
R1 Register 1
R2 Register 2
R3 Register 3
R4 Register 4
R5 Register 5
Stack pointer
R6 / SP Register 6 / Stack Pointer
Instruction pointer
R7 / PC Register 7 / Program Counter
Status flags
I V N Z C Processor Status Word
Floating Point Status Register

The CPU contained eight general-purpose 16-bit registers (R0 to R7). Register R7 was the program counter (PC). Although any register could be used as a stack pointer, R6 was the stack pointer (SP) used for hardware interrupts and traps.

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