3.3.12.2.1 DSP Multiply Instructions

The DSP instructions that use the multiplier are summarized in Table 3-21.

Table 3-21. DSP Instructions that Use the Multiplier
DSP Instruction⁽¹⁾	Description	Algebraic Equivalent
MAC	Multiply and Add to Accumulator or Square and Add to Accumulator	a = a + b c*
MSC	Multiply and Subtract from Accumulator	a = a – b c*
MPY	Multiply	a = b c*
MPYN	Multiply and Negate Result	a = -b c*
SQR	Square to Accumulator	a = b ^ 2
SQRAC	Square and Accumulate	a = a + (b ^ 2)
ED	Partial Euclidean Distance	a = (b – c)²
EDAC	Add Partial Euclidean Distance to the Accumulator	a = a + (b – c)²
Note: DSP instructions using the multiplier can operate in signed or unsigned fractional (1.15/1.31).

The DSP Multiplier Unsigned/Signed Control (US) bits (CORCON[12]) determine whether the DSP multiply instructions are signed (default) or unsigned. The US bits do not influence the MCU multiply instructions, which have specific instructions for signed or unsigned operation. If the USx bits are set to ‘01’, the input operands for instructions shown in Table 3-21 are considered as unsigned values, which are always zero-extended into the 33rd bit of the multiplier value. If the USx bits are set to ‘00’, the operands are sign-extended.

If the USx bits (CORCON[13:12]) are set to ‘10’, the operands for the instructions listed above are considered as unsigned values. The result is zero-extended prior to any operation with the accumulator (which will always effectively be signed).