PIC24FJ16MC101_12 Datasheet, PDF (30/350 Pages) Microchip Technology – 16-bit Microcontrollers (up to 32 KB Flash and 2 KB SRAM)

PIC24FJ16MC101/102 AND PIC24FJ32MC101/102/104
3.4 Arithmetic Logic Unit (ALU)
The PIC24FJ16MC101/102 and PIC24FJ32MC101/
102/104 ALU is 16 bits wide and is capable of addition,
subtraction, bit shifts, and logic operations. Unless oth-
erwise mentioned, arithmetic operations are 2’s com-
plement in nature. Depending on the operation, the
ALU may affect the values of the Carry (C), Zero (Z),
Negative (N), Overflow (OV), and Digit Carry (DC) Sta-
tus 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 reg-
ister array, or data memory, depending on the address-
ing 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 PIC24FJ16MC101/102 and PIC24FJ32MC101/
102/104 CPU incorporates hardware support for both
multiplication and division. This includes a dedicated
hardware multiplier and support hardware for 16-bit
divisor division.
3.4.1 MULTIPLIER
Using the high-speed 17-bit x 17-bit multiplier, the ALU
supports unsigned, signed or mixed-sign operation in
several 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
3.4.2 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. Sixteen-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.
3.4.3 MULTI-BIT DATA SHIFTER
The multi-bit data shifter is capable of performing up to
16-bit arithmetic or logic right shifts, or up to 16-bit left
shifts in a single cycle. The source can be either a
working register or a memory location.
The shifter requires a signed binary value to determine
both the magnitude (number of bits) and direction of the
shift operation. A positive value shifts the operand right.
A negative value shifts the operand left. A value of ‘0’
does not modify the operand.
DS39997C-page 30
Preliminary
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