DSPIC33FJ12MC02ESS datasheet(20/284 Pages) MICROCHIP

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dsPIC33FJ12MC201/202

DS70265B-page 18

Preliminary

2.5

Arithmetic Logic Unit (ALU)

The dsPIC33FJ12MC201/202 ALU is 16 bits wide and

is capable of addition, subtraction, bit shifts and logic

operations. Unless otherwise mentioned, arithmetic

operations are 2’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 “dsPIC30F/33F Programmer’s Reference

Manual” (DS70157) for information on the SR bits

affected by each instruction.

The dsPIC33FJ12MC201/202 CPU incorporates hard-

ware support for both multiplication and division. This

includes a dedicated hardware multiplier and support

hardware for 16-bit-divisor division.

2.5.1

MULTIPLIER

Using the high-speed 17-bit x 17-bit multiplier of the

DSP engine, 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 unsigned 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

2.5.2

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.

2.6

DSP Engine

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

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

subtracter (with two target accumulators, round and

saturation logic).

The dsPIC33FJ12MC201/202 is a single-cycle instruc-

tion flow architecture; therefore, concurrent operation

of the DSP engine with MCU instruction flow is not pos-

sible. However, some MCU ALU and DSP engine

resources can be used concurrently by the same

instruction (e.g., ED, EDAC).

The DSP engine can also perform inherent accumula-

tor-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 or unsigned DSP multiply (US)

• 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)

A block diagram of the DSP engine is shown in

Figure 2-3.

TABLE 2-1:

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 = x 2

MPY.N

A = – x * y

MSC

A = A – x * y

Yes

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