AS8218 datasheet(91/123 Pages) AMSCO

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Data Sheet AS8218 / AS8228

Revision 3.0, 31-May-06

Page 91 of 123

Squareroot Block (SQRT)

This SQRT block calculates the square root of a 40 bit input value (mapped to 5 eight bit input registers).

The output is a 20 bit number which is mapped to 3 eight bit output registers.

The calculation starts immediately after the least significant byte has been written (= address E8h).

For the square root calculation the Gypsi- or radicand algorithm is used, which produces one bit per clock

cycle. Thus after 20 cycles the result is available in the SQRTOUT[2:0] registers.

Note: The interrupt signal is not connected to the interrupt controller of the MCU, because the result is

available after a defined period of 4 machine cycles. The programmer has to take care for the correct timing.

For instance, 4 NOP instructions must be inserted before reading out the result.

When writing SQRTIN[39:36] are don’t care.

When reading SQRTOUT[23:20] those bits equal zero.

Data Registers

SFR-Address

Name

Description

E8h

SQRTIN0

Input value[7:0]

E9h

SQRTIN1

Input value[15:8]

EAh

SQRTIN2

Input value[23:16]

EBh

SQRTIN3

Input value[31:24]

ECh

SQRTIN4

Input value[39:32]

EDh

SQRTOUT0

Output value[7:0]

EEh

SQRTOUT1

Output value[15:8]

EFh

SQRTOUT2

Output value[19:16]

MOV SQRT4, #...

MOV SQRT0, #...

MOV A, SQRT2, ...

4 cyc

square root

calculation

start calculation

result available

Figure 23: Timing diagram

During the time of calculation data must not be overridden. As soon as the register SQRT0 is written, the

calculation sequence is retriggered and the result is calculated from the latest contents of the 5 input registers.

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