Condition Code

The condition code is stored in the PSW as a 2-bit binary number, therefore it may contain the four values: 0, 1, 2, 3.

The branch-on-condition instructions BC and BCR contain a 4-bit immediate mask field.  The bit numbers of the mask bits correspond to the four CC values.  The instructions test the current CC for any of the values represented by the mask bits that equal B'1'.  If a match is found, the branch is taken.  Therefore, setting multiple 1-bits in the mask directs the instructions to take the branch for any of several condition codes.

CC	Mask	Coded Mask
0	1000	BC 8,DEST
1	0100	BC 4,DEST
2	0010	BC 2,DEST
3	0001	BC 1,DEST
0 or 3	1001	BC 9,DEST
Not 0	0111	BC 7,DEST
Not 3	1110	BC 14,DEST
Any	1111	BC 15,DEST
None	0000	BC 0,DEST

The branch extended-mnemonic B is implemented as the BC instruction with all 4 mask bits set to 1:

         B     DEST                      THE SAME INSTRUCTION
         BC    15,DEST

A null BC instruction takes effect for no value of CC.

         BC    0,DEST                    GOING NOWHERE

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