Bit Zero Test (BZT)/OP=40


OP AF BF A Syllable

OP = 40

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 or may indicate that the A syllable is a literal.
BF is the eight-bit selection mask. One bits in this mask select those bit positions to be tested for 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 examined. 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. See Compatibility Notes A.05.


The Bit Zero Test instruction tests a data field in memory A in eight-bit groups, for zero bits in the bit positions selected by the field mask BF.

If 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 EQUAL if any tested bit is zero or to HIGH if all tested bits are one bits.


Field overlap is not applicable to this instruction.


Example (1) Zero test - Zero found

OP AFBF A Syllable
40 04C0 A Field (UA)
                    BEFORE              AFTER
   A Field         C3C1B77B           unchanged
    MASK           C0C0C0C0
   Comparison Flags   nn                EQUAL

Example (2) Zero test - All ones found

OP AFBF A Syllable
40 04C0 A Field (UA)
                    BEFORE              AFTER
   A Field         C2D9C1C3           unchanged
    MASK           C0C0C0C0
   Comparison Flags   nn                 HIGH
instructions/bzt.txt · Last modified: 2008/11/25 12:21 by scott
Except where otherwise noted, content on this wiki is licensed under the following license: CC Attribution-Noncommercial-Share Alike 3.0 Unported
Recent changes RSS feed Donate Powered by PHP Valid XHTML 1.0 Valid CSS Driven by DokuWiki