Bit Reset (BRT)/OP=33


OP AF BF A Syllable

OP = 33

AF is the length of the A field. A value of 00 is equal to a length of 100 units (digits or characters as specified by the A address controller). AF may be indirect. A literal will cause an Invalid Instruction (IEX = 21) fault. See Compatibility Notes A.22.1.
BF is the eight-bit selection mask. One bits in this mask select those bit positions to be set to zero bits within each eight-bit group of the A data field. A through F may be used to specify undigits in the mask. The field will not be recognized as indirect.

The A Syllable is the address of the data field to be modified. Address may be indexed, indirect or extended. The final address controller data type must be UN or UA. Use of SN data type is will cause an Illegal Instruction (IEX = 03) fault.


The Bit Reset instruction resets bits in a data field in memory A in eight-bit groups according to the bit positions selected by one bits in the field mask BF.

If the UN format is specified and the number of digits accessed is even, the entire eight-bit mask is applied to successive groups of two digits. if the number of digits is odd, the operation is the same until the last digit is accessed. The most significant four bits of the mask are applied to this digit.

Comparison Flags

Set the Comparison Flags to HIGH if the least significant bit of the result is a one; otherwise, set the comparison flags to EQUAL.


There are no overlap restrictions for this instruction.


Example (1) Bit Reset - Alpha Field

OP AFBF A Syllable
33 03A0 A Field (UA)
                    BEFORE              AFTER
   A Field          F1F2F3             515253
    MASK            A0A0A0    
   Comparison Flags   nn                HIGH

Example (2) Bit Reset - Numeric Field

OP AFBF A Syllable
33 0515 A Field (UN)
                    BEFORE              AFTER
   A Field          43105               42004
    MASK            15151
   Comparison Flags   nn                EQUAL
instructions/brt.txt · Last modified: 2008/11/25 13:19 by scott
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