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8- 24 M68040 USER’S MANUAL MOTOROLA
8.4.6 Access Error Stack Frame (Format $7)
A 30-word access error stack frame is created for data and instruction access faults other
than instruction address errors. In addition to information about the current processor
status and the faulted access, the stack frame also contains pending write-backs that the
access error exception handler must complete. The following paragraphs describe in
detail the format for this frame and how the processor uses it when returning from
exception processing.
Stack Frames Exception Types Stacked PC Points To
SPECIAL STATUS WORD (SSW)
$00 WRITE-BACK 1 STATUS (WB1S)
015
SP
+$02
+$12
ACCESS ERROR STACK FRAME 
(30 WORDS)–FORMAT $7
FAULT ADDRESS (FA)
+$14
WRITE-BACK 3 ADDRESS (WB3A)
WRITE-BACK 3 DATA (WB3D)
WRITE-BACK 1 DATA/PUSH DATA LW0 (WB1D/PD0)
PUSH DATA LW 1 (PD1)
WRITE-BACK 2 ADDRESS (WB2A)
WRITE-BACK 2 DATA (WB2D)
WRITE-BACK 1 ADDRESS (WB1A)
PUSH DATA LW 2 (PD2)
PUSH DATA LW 3 (PD3)
+$18
+$1C
+$20
+$24
+$28
+$2C
+$30
+$34
+$38
STATUS REGISTER
PROGRAM COUNTER
0 1 1 1 VECTOR OFFSET
EFFECTIVE ADDRESS (EA)
$00 WRITE-BACK 2 STATUS (WB2S)
$00 WRITE-BACK 3 STATUS (WB3S)
+$10
+$0C
+$0E
+$08
+$0A
+$06
Data or Instruction Access
Fault (ATC Fault or Bus
Error)
Next Instruction
8.4.6.1 EFFECTIVE ADDRESS. The effective address contains address information when
one of the continuation flags CM, CT, CU, or CP in the SSW is set.
8.4.6.2 SPECIAL STATUS WORD (SSW). The SSW information indicates whether an
access to the instruction stream or the data stream (or both) caused the fault and contains
status information for the faulted access. Figure 8-7 illustrates the SSW format.
1514131211109876543210
CP CU CT CM MA ATC LK RW X SIZE TT TM
Figure 8-7. Special Status Word Format
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