ALS31313 datasheet(21/25 Pages) ALLEGRO

21 / 25 page

Automotive Grade, 3-D Linear Hall-Effect Sensor

with I2C Output and Advanced Low Power Management

ALS31313

Allegro MicroSystems, LLC

955 Perimeter Road

Manchester, NH 03103-3353 U.S.A.

www.allegromicro.com

I2C CRC Byte

The ALS31313 CRC feature is enabled by setting the I2C CRC

Enable bit, Address 0x02, bit 18. When enabled, the ALS31313

read transaction returns one extra byte corresponding the CRC

calculation of that read. The bytes of the I2C read sequence used

for CRC calculation are:

1. 8-Bit Register Address

2. The 7-Bit Slave Address + Read bit (1’b1)

3. The four Data Bytes (32 Bits, MSB first)

The code is 8 bits in length and will be generated using the

CRC8-ATM (0x83) polynomial:

p(x) = x8 + x2 + x + 1

Table 17: Example CRC Calculation Result

Slave Address

Address

Data

CRC

0xC3

0x28

0x282A2C80

0xEC

0xC3

0x28

0x282A2C00

0x65

I2C Readback Modes

The ALS31313 supports three different readback modes over the

I2C interface, including single, fast loop, and full loop modes.

These modes simplify the process of repeatedly polling the

ALS31313 for magnetic X, Y, Z, and Temperature data.

Readback modes on the ALS31313 are described in Table 18. The

desired readback mode may be entered by setting the appropriate

bits for I2C Loop Mode, address 0x27, bits 3:2.

Table 18: ALS31313 Looping Read Modes

Code

(Binary)

Mode

Description

‘00’

Single

No Looping. Similar to Default I2C.

‘01’

Fast Loop

X, Y, Z, and Temperature fields are looped.

8 MSBs for X, Y, and Z, 6 MSBs for

Temperature are looped.

‘10’

Full Loop

X, Y, Z, and Temperature fields are looped.

Full 12-bit resolution fields are looped.

‘11’

Single

Same as code 0.

SINGLE MODE

A single write or read command to any register—this is the

default mode and is best suited for setting fields and reading

static registers. If desired, this mode can be used to read X, Y, Z,

and Temperature data in a typical serial fashion, but fast or full

loop read modes are recommended for high-speed data retrieval.

FAST LOOP MODE

Fast Loop Mode offers continuous reading of X, Y, Z, and tempera-

ture values, but is limited to the upper 8 bits of X, Y, and Z, and

upper 6 bits of Temperature. This mode is intended to be a time

efficient way of reading data from the IC at the expense of truncat-

ing resolution. The flow chart in Figure 7 depicts Fast Loop Mode.

Figure 7: Fast Loop Mode

FULL LOOP MODE

Full Loop Mode provides continuous reads of X, Y, Z, and Tem-

perature data with full 12-bit resolution. This is the recommended

mode for applications that require a higher data rate for X, Y, Z,

and Temperature with full resolution. The flow chart in Figure 8

depicts Full Loop Mode.

Figure 8: Full Loop Mode

ALS31313

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