AN2388 datasheet(39/54 Pages) STMICROELECTRONICS

39 / 54 page

AN2388

Software design

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div_q31_q15_q15( short LeftOpMsb, short LeftOpLsb, short RightOp, short *Output)

where:

LeftOpMsb

Left operand most significant bits

LeftOpLsb

Left operand least significant bits

RightOp

Right operand

Output

Output pointer

Assembly source code:

div_q31_q15_q15.asm

Code size and cycles:

Size: 98 bytes

Instruction cycles: 216

Note:

The dividend must be smaller than the divisor for a valid result.

Divisions on limits (for example, division of 1 by 1 or of -1 by -1) are not computed by this

routine.

The algorithm implemented does not allow integer division. For dividing two integers

(dividend in 32.0 format and divisor in 16.0), shift the dividend one bit to the left (into 31.1

format) before dividing.

4.5

Analog value scaling

The AC induction motor vector control application uses a fractional representation for all real

quantities, except time. The following equation shows the relationship between a real and a

fractional representation:

4.5.1

Current sensing and scaling

The FOC algorithm requires two phase currents as input. In this application a current

voltage transducer Hall effect based (LEM type) sense these two current. The current

sensor output therefore needs to be rearranged and scaled so that it can be used by the

control software as q1.15 format values

Figure 33.

Current sensing block diagram

Note that the real quantity range used in the fractional value represents the maximum

measurable current, which is not necessarily equal to the maximum phase current. This is

Range

Quantity

Value

Fractional

Scaling

Factor (q1.15)

Range

adjustment

A/D

Conditioning

circuitry

iphase

Current Sensor

ST10F2756

ifractional value

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