AT&T 3B2/300 Technical Reference Manual page 293

FUNCTIONAL D E S C R I P T I O N - - - - - - - - - - - - - - - - - - - - - - - - - - -
ISC Bits 06-03 are the Internal State Code (ISC) bits. The ISC bits are used to
distinguish between exceptions of the same type. This field is used with the
Exception Type (ET) field to determine when exception occurred. Traps, exceptions,
and faults are equivalent with respect to ISC. Normal exceptions are decoded on a
priority scheme if more than one occurs in a particular cycle. Exceptional
conditions that reset the PSW flags are indicated by an asterisk
(*)
in the following
data.
EXCEPTION ISC BITS
TYPE EXCEPTION 6543
NORMAL INTEGER ZERO-DIVIDE
o o o o•
EXCEPTION TRACE TRAP 0 0 0 1
(ET=l l)
ILLEGAL OPCODE 0 0 1 0
RESERVED OPCODE 0 0 1 1
INVALID DESCRIPTOR
o
1
o o•
EXTERNAL MEMORY FAULT 0 1 0 1
GATE VECTOR FAULT 0 1 1 0
ILLEGAL LEVEL CHANGE 0 1 1 1
RESERVED DAT A TYPE 1
o o o•
INTEGER OVERFLOW 1 0 0 1
PRIVILEGED OPCODE 1 0 1 0
BREAKPOINT TRAP 1 0 1 1
PRIVILEGED REGISTER 1 1 1 1
STACK
STACK BOUND 0000
EXCEPTION STACK FAULT 0 0 0 1
(ET=lO) •
INTERRUPT ID FETCH 0 0 1 0
PROCESS OLD PCB FAULT 0000
EXCEPTION GATE PCB FAULT 0 0 0 1
(ET=Ol)
NEW PCB FAULT 0 1 0 0
RESET
OLD PCB FAULT 0000
EXCEPTION SYSTEM DATA 0 0 0 1
(ET=OO)
INTERRUPT STACK FAULT 0 0 1 0
EXTERNAL RESET 0 0 1 1
NEW PCB FAULT 0 1 0 0
GATE VECTOR FAULT 0 1 1 0
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