DSPIC30F3012AT20ESLASHML datasheet(22/205 Pages) MICROCHIP

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PIC30F2011/2012/3012/3013

DS70139E-page 20

2.3

Divide Support

The dsPIC DSC devices feature a 16/16-bit signed

fractional divide operation, as well as 32/16-bit and 16/

16-bit signed and unsigned integer divide operations, in

the form of single instruction iterative divides. The fol-

lowing instructions and data sizes are supported:

DIVF

- 16/16 signed fractional divide

DIV.sd

- 32/16 signed divide

DIV.ud

- 32/16 unsigned divide

DIV.s

- 16/16 signed divide

DIV.u

- 16/16 unsigned divide

The 16/16 divides are similar to the 32/16 (same number

of iterations), but the dividend is either zero-extended or

sign-extended during the first iteration.

The divide instructions must be executed within a

REPEAT

loop. Any other form of execution (e.g., a

series of discrete divide instructions) will not function

correctly because the instruction flow depends on

RCOUNT. The divide instruction does not automatically

set up the RCOUNT value and it must, therefore, be

explicitly and correctly specified in the REPEAT instruc-

tion, as shown in Table 2-1 (REPEAT executes the tar-

get instruction {operand value+1} times). The REPEAT

loop count must be setup for 18 iterations of the DIV/

DIVF

instruction. Thus, a complete divide operation

requires 19 cycles.

TABLE 2-1:

DIVIDE INSTRUCTIONS

Note:

The divide flow is interruptible. However,

the user needs to save the context as

appropriate.

Instruction

Function

DIVF

Signed fractional divide: Wm/Wn

→ W0; Rem → W1

DIV.sd

Signed divide: (Wm+1:Wm)/Wn

→ W0; Rem → W1

DIV.s

Signed divide: Wm/Wn

→ W0; Rem → W1

DIV.ud

Unsigned divide: (Wm+1:Wm)/Wn

→ W0; Rem → W1

DIV.u

Unsigned divide: Wm/Wn

→ W0; Rem → W1

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