CNOP
CNOP is used to align any instruction or storage area on a specific boundary.
Format: CNOP byte,word
byte is an absolute expression that specifies at which even numbered byte in a fullword or doubleword the location counter is set to.
fullword: the value of the expression must be 0 or 2
doubleword: the value of the expression must be 0, 2, 4, or 6
word is an absolute expression that specifies whether byte is a fullword or a doubleword
fullword: the value of the expression must be 4
doubleword: the value of the expression must be 8
Valid CNOP values: (also on page 19 of your yellow card)
byte,word alignment 0,4 beginning of a fullword 2,4 middle of a fullword 0,8 beginning of a doubleword 2,8 second halfword of a doubleword 4,8 middle (third halfword) of a doubleword 6,8 fourth halfword of a doubleword
The location counter value is not altered if it is already aligned correctly.
Alignment is achieved by filling in the skipped bytes with no-operation instructions (BCR 0,0)