Xerox 550 - Page 31

Instruction in memory:
o 1 2
Instruction in instruction register:
Indi rect
reference addresses:
Contents
of indirect reference address:
Address used if bit 0 = 1:
Displacement
aligned for halfword indexing:
Final
effective address:
Figure
9. Generation of Effective Virtual Address (Indirect Real-Extended Addressing)
The
stack pointer doubJeword for push-down instructions
contains a 2O-bit word address for the top of stack address
field; as shown in the following format:
24 Me i n Memory
During real-extended addressing memory write protection
is invoked.
Table 1 summarizes the addressing
characteristics.