HLASM - BNOR = Branch on Not Ones / Overflow Register

The opcode of the BNOR extended mnemonic is X'07' with mask B'1110'.

The mask is the third hex digit of the instruction, and - though this is uncommon - can be regarded as the third hex digit of the opcode as well.

BNOR is used both for Branch on Not Ones Register and for Branch on Not Overflow Register

Usage

  1. Perform a branch if the condition code is not 3 or B'11', meaning either "all ones" or "overflow".
  2. Condition code 3 may occur after bit operations, such as TM. Do not use after boolean operations (and, or, exclusive or) since these do not set condition code 3.
  3. Condition code 3 may also occur after signed binary calculations, such as AR. Do not use after multiplication or division, since these do not set condition code 3.

Arguments

  1. Register holding the destination address.

Function

  1. The processor uses the PSW's two-bit condition code as an index into the 4-bit condition mask.
  2. If the selected mask-bit is one, then it branches to the address specified in the second argument. If the bit is zero, then the processor continues with the next instruction.
  3. The condition code does not change.

Special Cases

  1. If the destination address is in register 0 no branch will be taken.

Related Instructions

  1. BNO branches to a location that is directly addressable in base-displacement form.
  2. BCR is the real instruction associated with this extended mnemonic.

Hardware

  1. All hardware supports the BNOR instruction.

Remarks

  1. The PSW's Amode setting determines how many bits are used for the destination address.

Examples

         YREGS                          * Define register names
         ...
         TM    FIELD,MASK               * Check bit settings
         BNOR  R14                      * Ok, Return
         ...
         AR    R6,R1                    * Add to total
         BNOR  R11                      * Ok: skip overflow logic
         ...

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