Take Midinstruction Exception Primitive - Motorola MC68020 User Manual

which instruction the coprocessor was executing when the exception occurred. A
coprocessor can record the instruction address by setting PC = 1 in one of the primitives it
uses before releasing the main processor.

7.4.19 Take Midinstruction Exception Primitive

The take midinstruction exception primitive initiates exception processing using a
coprocessor-supplied exception vector number and the midinstruction exception stack
frame format. This primitive applies to general and conditional category instructions.
Figure 7-42 shows the format of the take midinstruction exception primitive.
15 14 13
0 PC
Figure 7-42. Take Midinstruction Exception Primitive Format
The take midinstruction exception primitive uses the PC bit as described in 7.4.2
Coprocessor Response Primitive General Format. The vector number field contains
the exception vector number used by the main processor to initiate exception processing.
When the main processor receives this primitive, it acknowledges the coprocessor
exception request by writing an exception acknowledge mask (refer to 7.3.2 Control CIR)
to the control CIR. The MC68020/EC020 then performs exception processing as
described in Section 6 Exception Processing. The vector number for the exception is
taken from the vector number field of the primitive, and the MC68020/EC020 uses the
10-word stack frame format shown in Figure 7-43.
SP
Figure 7-43. MC68020/EC020 Midinstruction Stack Frame
7-48
12 11 10 9
0 1 1 1 0
15 12 11
+02
0 0
+06 1 1
+08
+0C
+0E
+10
M68020 USER'S MANUAL
8 7
1 VECTOR NUMBER
STATUS REGISTER
SCAN PC
VECTOR NUMBER
PROGRAM COUNTER
INTERNAL REGISTER
OPERATION WORD
EFFECTIVE ADDRESS
0
0
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