DSPIC33FJ16GP101_13 Datasheet, PDF (43/386 Pages) Microchip Technology – 16-Bit Digital Signal Controllers up to 32-Kbyte Flash and 2-Kbyte SRAM

dsPIC33FJ16(GP/MC)101/102 AND dsPIC33FJ32(GP/MC)101/102/104
3.5 Arithmetic Logic Unit (ALU)
The
dsPIC33FJ16(GP/MC)101/102
and
dsPIC33FJ32(GP/MC)101/102/104 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), Over-
flow (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
dsPIC33FJ16(GP/MC)101/102
and
dsPIC33FJ32(GP/MC)101/102/104 CPU incorpo-
rates hardware support for both multiplication and
division. This includes a dedicated hardware multiplier
and support hardware for 16-bit-divisor division.
3.5.1 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
3.5.2 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. The 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.
3.6 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
dsPIC33FJ16(GP/MC)101/102
and
dsPIC33FJ32(GP/MC)101/102/104 is a single-cycle
instruction flow architecture; therefore, concurrent
operation of the DSP engine with MCU instruction flow
is not possible. 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 3-3.
TABLE 3-1:
Instruction
CLR
ED
EDAC
MAC
MAC
MOVSAC
MPY
MPY
MPY.N
MSC
DSP INSTRUCTIONS
SUMMARY
Algebraic
Operation
ACC Write
Back
A=0
Yes
A = (x – y)²
No
A = A + (x – y)²
No
A = A + (x * y)
Yes
A = A + x²
No
No change in A
Yes
A=x*y
No
A=x²
No
A=–x*y
No
A=A–x*y
Yes
 2011-2012 Microchip Technology Inc.
DS70652E-page 43