DSPIC30F datasheet(16/220 Pages) MICROCHIP

16 / 220 page

dsPIC30F5011/5013

DS70116C-page 14

Preliminary

 2004 Microchip Technology Inc.

2.3

Divide Support

The dsPIC 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 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.sw

- 16/16 signed divide

DIV.uw

- 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 will execute 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.sw or

DIV.s

Signed divide: Wm/Wn

→ W0; Rem → W1

DIV.ud

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

→ W0; Rem → W1

DIV.uw or

DIV.u

Unsigned divide: Wm/Wn

→ W0; Rem → W1

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