Datasheet

dsPIC33EPXXX(GP/MC/MU)806/810/814 and PIC24EPXXX(GP/GU)810/814
DS70616F-page 46 Preliminary © 2009-2012 Microchip Technology Inc.
3.8 Arithmetic Logic Unit (ALU)
The 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
register array or data memory, depending on the
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” (DS70157) 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:
1. 32-bit signed/16-bit signed divide
2. 32-bit unsigned/16-bit unsigned divide
3. 16-bit signed/16-bit signed divide
4. 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 (dsPIC33EPXXX(GP/
MC/MU)806/810/814 Devices Only)
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 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, unsigned, or mixed-sign 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 (ACC-
SAT)
TABLE 3-2: DSP INSTRUCTIONS
SUMMARY
Instruction
Algebraic
Operation
ACC Write
Back
CLR A = 0
Yes
ED A = (x – y)
2
No
EDAC A = A + (x – y)
2
No
MAC A = A + (x • y) Yes
MAC A = A + x
2
No
MOVSAC No change in A Yes
MPY A = x • y No
MPY A = x
2
No
MPY.N A = – x • y No
MSC A = A – x • y Yes