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There are two formats for machine instructions. Most instructions have the format:
000000000 0111 1 1111 112222222222333333 012345678 9012 3 4567 890123456789012345 ________________________________________ | | | | | | | OP | AC |I| X | Y | |_________|____|_|____|__________________|Input-output instructions (which are illegal in user mode) have the format: (These instructions are not discussed any farther by this file).
000 0000000 111 1 1111 112222222222333333 012 3456789 012 3 4567 890123456789012345 _________________________________________ | | | | | | | |111| DEV |IOP|I| X | Y | |___|_______|___|_|____|__________________|In the diagrams above the field names are
OP = operation code AC = accumulator field I = indirect bit X = index field Y = address field DEV = device code IOP = input-output operation codeSome example intructions are:
MOVE 1,@100 ;MOVE is the OP. AC is 1. ;@ sets the I bit. ;X is zero, Y is 100. HRRZ 17,1(3) ;HRRZ is the OP. AC is 17, ;Y = 1, X = 3, I = 0 SOS FOO ;SOS is OP, FOO is symbolic ;for the Y field. AC, X, I are 0.The address field, the index field, and the indirect bit are all used in effective address computation. See also Addr-Comp.