NAR 2 - Addressing Modes

Addressing Modes

With four address mode selection bits (P, R, I and N - indexed, relative, indirect and immediate), NAR 2 instructions can specify 16 different addressing modes but not all make sense in all instructions. In the following table:

M specifies the 32-bit value (content) of memory location x
BN specifies the program counter
p specifies the 16-bit signed parameter at location
Xi specifies the index register selected by data at location
f is the "effective value" function used for indirect addressing (see details below):

Addr. flags				Instruction type
P	R	I	N	Data	Jump
-	-	-	-	M	p
-	-	-	N	p	p
-	-	I	-	M)]	f(M)
-	-	I	N	f(M)	f(M)
-	R	-	-	M	BN+p
-	R	-	N	BN+p	BN+p
-	R	I	-	M)]	f(M)
-	R	I	N	f(M)	f(M)
P	-	-	-	M	Xi+p
P	-	-	N	Xi+p	Xi+p
P	-	I	-	M)]	f(M)
P	-	I	N	f(M)	f(M)
P	R	-	-	M	BN+Xi+p
P	R	-	N	BN+Xi+p	BN+Xi+p
P	R	I	-	M)]	f(M)
P	R	I	N	f(M)	f(M)

Note 1: "N" (immediate) flag has no effect on jump (flow control) instructions, as the processor can not jump into a specified value, but only to a memory address.

Famous quotes containing the words addressing and/or modes:

“A writer who writes, “I am alone” ... can be considered rather comical. It is comical for a man to recognize his solitude by addressing a reader and by using methods that prevent the individual from being alone. The word alone is just as general as the word bread. To pronounce it is to summon to oneself the presence of everything the word excludes.”
—Maurice Blanchot (b. 1907)

“Without any extraordinary effort of genius, I have discovered that nature was the same three thousand years ago as at present; that men were but men then as well as now; that modes and customs vary often, but that human nature is always the same. And I can no more suppose, that men were better, braver, or wiser, fifteen hundred or three thousand years ago, than I can suppose that the animals or vegetables were better than they are now.”
—Philip Dormer Stanhope, 4th Earl Chesterfield (1694–1773)