A31316 datasheet(39/61 Pages) ALLEGRO

39 / 61 page

3D Magnetic Position Sensor IC

A31316

Allegro MicroSystems

955 Perimeter Road

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

www.allegromicro.com

During a read command, the device determines the baud rate

from the sync bits and responds with a read response frame using

the same baud rate detected. The baud rate during a write com-

mand is also automatically detected, but is only used for decod-

ing, as the A31316 does not respond to write commands.

Table 26: Manchester Bit Definition (device response)

Quantity

of Bits

Name

Values

Description

Synchronization

Used to announce the

beginning of a Manchester

interface response

Data

Any

Read data

CRC

Any

Bits to check the validity of

frame.

The device memory contains non-volatile (EEPROM) and vola-

tile registers which are accessible via the serial interface through

Manchester communication modes. The memory address space is

divided into Factory and Customer areas.

MANCHESTER UNLOCKING – VIA OVD

1. At any time after POR, create an OVD condition. This sets

the OUT in HIGH-Z state since PWM/SENT Output is turned

off.

2. Send the correct access code.

3. Device is unlocked.

4. If manch_en bit was set LOW, the OVD condition can be

removed and the device returned to PWM/SENT Mode with

the device unlocked. OVD is needed for every Manchester

Read/Write command.

5. If manch_en bit was set HIGH, the OVD condition can be

removed, but the device will remain in communication mode.

OVD is not needed for Manchester transactions until manch_

en bit is set LOW through a Write Command. This action will

lock the device back.

MANCHESTER UNLOCKING – VIA TRIGGERING

PULSE

1. At any time after POR, create the trigger condition by driving

the output LOW for a specific amount of time depending

on the PWM (minimum of 2 full PWM messages) or SENT

Mode (minimum of 30 ttick). Then release the line or drive it

HIGH to create a 0→1 condition.

2. The device is in communication mode and a 300 µs timeout

starts.

3. Write the correct access code before the 300 µs expires. Tim-

ing requirements stop once the first sync bit is detected.

4. If the code is wrong, aborted, or it was an incorrect transac-

tion, the part goes back to PWM/SENT mode. Retrying by

starting at step 1 is possible.

5. If the code is correct, the device is unlocked and manch_en

bit is set to 1. The output is disabled, and the device remains

unlocked until manch_en is written to 0 through a Manches-

ter Write.

Table 27: Unlock Code and Customer Access Codes

Command

Write address

Write data

Customer access code

(Read access to factory)

manch_en = 1

0x86

0xC2D8E67B

Customer access code

(Read access to factory)

manch_en = 0

0x86

0xC2D8E67A

Manchester Communication CRC

The serial interface uses a cyclic redundancy check (CRC) for

data-bit error checking (synchronization bits are ignored during

the check). The CRC algorithm is based on the following polyno-

mial and the calculation is represented graphically in Figure 28.

The trailing 3 bits of a message frame comprise the CRC token.

The CRC is initialized at 111.

g(x) = x3 + x + 1

Input Data

1x0

1x1

0x2

1x3

= x3 + x +1

Figure 28: Manchester CRC Implementation

EEPROM Lock

There are 3 different lock modes available in the A31316:

EELOCK, WRLOCK, and FLOCK. Each of these are separate

from access lock which requires a customer unlock code to con-

trol. EELOCK locks the EEPROM from external write access,

while still allowing writes to shadow and volatile registers.

The entirety of memory can still be read in this mode allowing

for a level of customer lock, while maintaining debug support.

WRLOCK prevents any write both EEPROM and volatile regis-

ters. Factory read support is maintained. This is not recommended

for any output mode. The FLOCK mode locks out both reads

and writes to EEPROM and all registers. This is will prevent any

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