ADMT4000 Multi-Turn GMR Counter Behaviour after 46-Turn Reset

Hello,

I am evaluating the ADMT4000 for an industrial absolute multi-turn encoder application.

I have successfully implemented:

• Angle reading
• LUT linearization
• Fault monitoring
• Radius monitoring
• Multi-turn reading using register 0x04 (ABSANGLE)

I am currently investigating the behavior of the GMR multi-turn counter and the D13 (TURN_CROSS) fault.

Test setup

• ADMT4000
• Diametrical magnet
• Magnetic field within specification (approximately 24 mT)
• D14 (AMR_RADIUS) = 0
• D9 (GMR_FALSE) = 0
• D13 (TURN_CROSS) monitored continuously

Test 1: 46-turn reset procedure

I rotated the shaft more than 46 turns CW.

After power-up:

WHOLE_TURNS = 46
D13 = 0

This appears to be the expected reset state.

Test 2: One turn CCW while powered

Starting from:

WHOLE_TURNS = 46
D13 = 0

I rotated exactly 1 turn CCW while the device remained powered.

Result:

WHOLE_TURNS = 45
D13 = 1

The turn counter changed correctly from 46 to 45, but TURN_CROSS became active.

Test 3: Conversion restart

I implemented a software command that:

1. Aborts conversion
2. Restarts conversion
3. Clears faults

After executing this procedure:

WHOLE_TURNS = 46
D13 = 0

The device returned to 46 turns.

Test 4: One turn CCW with power removed

Starting from:

WHOLE_TURNS = 46
D13 = 0

I completely removed:

• VDD
• VDRIVE

Then I rotated the shaft exactly 1 turn CCW while the device was unpowered.

After restoring power:

WHOLE_TURNS = 46
D13 = 0

The expected value would have been:

WHOLE_TURNS = 45
D13 = 0

but the counter remained at 46.

Questions

1. Is the "46-turn CW reset" procedure intended only to clear the GMR counter, or should it also establish a valid multi-turn reference for subsequent operation?
2. After a successful 46-turn reset, should a CCW rotation performed while the device is unpowered be reflected in the WHOLE_TURNS value after power-up?
3. Under which conditions is D13 (TURN_CROSS) expected to become active when the WHOLE_TURNS counter remains inside the valid 0...46 turn range?
4. Is an additional magnetic reset procedure (315° position with >60 mT field) required after the 46-turn reset procedure to obtain correct true power-on multi-turn operation?

Any clarification regarding the proper commissioning sequence for reliable GMR multi-turn operation would be greatly appreciated.

Thank you very much.