© Thomas Kunz 2000
SCE 574
84
Flags (cont.)
äOF
- overflow flag
äFor unsigned arithmetic - set iff result can not be represented in
fixed width
äFor
signed arithmetic: set iff carry into msbit differs from carry out of
msbit
äSet
iff a carry/borrow into/from the msbit but not into/from the fictitious bit
above the msbit OR a carry/borrow into/from the fictitious bit above the
msbit but
not into/from the msbit
ä3
Control flags
äTF - single step trap flag - if set - single step
interrupt occurs after execution of next instruction, TF is cleared by the single
step interrupt
äIF
- interrupt flag - if set - CPU will recognize maskable interrupts
äDF - direction flag - controls auto increment/decrement
of
index register on string instructions - is set - then auto-decrement