SUB ACC,loc16 <<T
6-335
SUB ACC,loc16 <<T Subtract Shifted Value From Accumulator
SYNTAX OPTIONS OPCODE OBJMODE RPT CYC
SUB ACC,loc16 <<T 0101 0110 0010 0111
0000 0000 LLLL LLLL
1 Y N+1
Operands ACC Accumulator register
loc16 Addressing mode (see Chapter 5)
T Upper 16−bits of the multiplicand register, XT(31:16)
Description Subtract from the ACC register the left−shifted contents of the 16-bit location
pointed to by the “loc16” addressing mode. The shift value is specified by the
four least significant bits of the T register, T(3:0) = shift value = 0..15. Higher
order bits are ignored. The shifted value is sign extended if sign extension
mode is turned on (SXM=1) else the shifted value is zero extended (SXM=0).
The lower bits of the shifted value are zero filled:
if(SXM = 1) // sign extension mode enabled
ACC = ACC − S:[loc16] << T(3:0);
else // sign extension mode disabled
ACC = ACC − 0:[loc16] << T(3:0);
Flags and
Modes
Z
After the subtraction, the Z flag is set if the ACC value is zero, else Z is
cleared.
N
After the subtraction, the N flag is set if bit 31 of the ACC is 1, else N is
cleared.
C
If the subtraction generates a borrow, C is cleared; otherwise C is set.
V
If an overflow occurs, V is set; otherwise V is not affected.
OVC
If(OVM = 0, disabled) then if the operation generates a positive overflow,
then the counter is incremented and if the operation generates a negative
overflow, then the counter is decremented. If(OVM = 1, enabled) then the
counter is not affected by the operation.
SXM
If sign extension mode bit is set; then the 16-bit operand, addressed by the
”loc16” field, will be sign extended before the addition. Else, the value will be
zero extended.
OVM
If overflow mode bit is set; then the ACC value will saturate maximum
positive (0x7FFF FFFF) or maximum negative (0x8000 0000) if the
operation overflowed.
Repeat If this operation is repeated, then the instruction will be executed N+1 times.
The state of the Z, N, C flags will reflect the final result. The V flag will be set if
an intermediate overflow occurs. The OVC flag will count intermediate
overflows, if overflow mode is disabled.
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