DSPIC33EP128GS708 datasheet(32/484 Pages) MICROCHIP

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dsPIC33EPXXXGS70X/80X FAMILY

DS70005258C-page 32

 2016-2018 Microchip Technology Inc.

3.8

Arithmetic Logic Unit (ALU)

The dsPIC33EPXXXGS70X/80X family ALU is 16 bits

wide and is capable of addition, subtraction, bit shifts and

logic operations. Unless otherwise mentioned, arithmetic

operations are two’s complement in nature. Depending

on the operation, the ALU can affect the values of the

Carry (C), Zero (Z), Negative (N), Overflow (OV) and

Digit Carry (DC) Status bits in the SR register. The C

and DC Status bits operate as Borrow and Digit Borrow

bits, respectively, for subtraction operations.

The ALU can perform 8-bit or 16-bit operations,

depending on the mode of the instruction that is used.

Data for the ALU operation can come from the W

addressing mode of the instruction. Likewise, output

data from the ALU can be written to the W register array

or a data memory location.

Refer to the “16-Bit MCU and DSC Programmer’s

Reference Manual” (DS70000157) for information on

the SR bits affected by each instruction.

The core CPU incorporates hardware support for both

multiplication and division. This includes a dedicated

hardware multiplier and support hardware for 16-bit

divisor division.

3.8.1

MULTIPLIER

Using the high-speed, 17-bit x 17-bit multiplier, the ALU

supports unsigned, signed or mixed-sign operation in

several MCU Multiplication modes:

• 16-bit x 16-bit signed

• 16-bit x 16-bit unsigned

• 16-bit signed x 5-bit (literal) unsigned

• 16-bit signed x 16-bit unsigned

• 16-bit unsigned x 5-bit (literal) unsigned

• 16-bit unsigned x 16-bit signed

• 8-bit unsigned x 8-bit unsigned

3.8.2

DIVIDER

The divide block supports 32-bit/16-bit and 16-bit/16-bit

signed and unsigned integer divide operations with the

following data sizes:

• 32-bit signed/16-bit signed divide

• 32-bit unsigned/16-bit unsigned divide

• 16-bit signed/16-bit signed divide

• 16-bit unsigned/16-bit unsigned divide

The quotient for all divide instructions ends up in W0

and the remainder in W1. 16-bit signed and unsigned

DIV instructions can specify any W register for both

the 16-bit divisor (Wn) and any W register (aligned)

pair (W(m + 1):Wm) for the 32-bit dividend. The divide

algorithm takes one cycle per bit of divisor, so both

32-bit/16-bit and 16-bit/16-bit instructions take the

same number of cycles to execute.

3.9

DSP Engine

The DSP engine consists of a high-speed 17-bit x 17-bit

multiplier, a 40-bit barrel shifter and a 40-bit adder/

subtracter (with two target accumulators, round and

saturation logic).

The DSP engine can also perform inherent accumulator-

to-accumulator operations that require no additional

data. These instructions are, ADD, SUB and NEG.

The DSP engine has options selected through bits in

the CPU Core Control register (CORCON), as listed

below:

• Fractional or Integer DSP Multiply (IF)

• Signed, Unsigned or Mixed-Sign DSP Multiply

(USx)

• Conventional or Convergent Rounding (RND)

• Automatic Saturation On/Off for ACCA (SATA)

• Automatic Saturation On/Off for ACCB (SATB)

• Automatic Saturation On/Off for Writes to Data

Memory (SATDW)

• Accumulator Saturation mode Selection

(ACCSAT)

TABLE 3-2:

DSP INSTRUCTIONS

SUMMARY

Instruction

Algebraic

Operation

ACC

Write-Back

CLR

A = 0

Yes

A = (x – y)2

EDAC

A = A + (x – y)2

MAC

A = A + (x • y)

Yes

MAC

A = A + x2

MOVSAC

No change in A

Yes

MPY

A = x • y

MPY

A = x2

MPY.N

A = – x • y

MSC

A = A – x • y

Yes

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