DSPIC30F2011 datasheet(22/206 Pages) MICROCHIP

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PIC30F2011/2012/3012/3013

DS70139F-page 22

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 opera-

tions, in the form of single instruction iterative divides.

The following 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

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 instruction, as shown in Table 2-1 (REPEAT

executes the target 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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