HP 3000 III Series Manual page 142

Machine Instructions and Stack Operations
For P relative mode, control is transferred unconditionally to P
+/- displacement, plus (if specified) the value in X; may be in-
direct. For DB, Q, and S relative modes, control is transferred
indirectly (only) via the location specified by DB, Q, or S +/-
this displacement; the content of the location so specified is
added to PB (plus post-indexing if X is specified) to obtain the
effective address for P.
Instruction Commentary 3.
Memory opcode: 14, bits 5,6
=
00, 10, or 11
Indicators: Unaffected
Addressing modes: P relative (+/-), direct or indirect
DB+ relative, indirect
Q+ relative, indirect
Q-
relative, indirect
S- relative, indirect
Indexing available
Traps: BNDV, BNDV on P and P relative if user or privileged
4-9. Move Instructions
Note
All Move instructions are interruptable af-
ter each word (or byte) transfer and will
continue from the point of interrupt when
control is returned to the instruction.
CMPB Compare By tes
PB/DB
'--v--'
SDEC
This instruction scans two byte strings simultaneously until the
compared bytes are unequal or until a specified number of compar-
isons have been made. CMPB expects a signed byte count in A, a
DB or PB relative displacement for a source byte address in B,
and a DB relative displacement for a target byte address in C.
As long as the word count in A has not been counted to zero, the
comparison proceeds as follows: The content of the byte address
loca tion specified by DB + B or PB + B is compared wi th the con-
tent of the byte address location specified by DB + C. If the
byte count in A is positive, the source and target displacement
values in Band C are incremented by one after each comparison,
and the byte count is decremented by one. If the byte count in A
is negative, the source and target displacement values in Band C
are decremented by one after each comparison, and the byte count
is incremented by one. Note that the byte count is always chang-
ed by one toward zero. The instruction terminates when either a
compar ison fa ils or the byte count in the TOS reaches ze ro. The
Condition Code is set to a
s~ecial
pattern to indicate the term-
inating condition. On termlnation, the instruction deletes from
the stack the number of words (0, 1, 2, or 3) specified by the
4-12