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Product data sheet

Rev. 05 — 16 August 2005

6 of 31

Philips Semiconductors

KMA200

Programmable angle sensor

Diagnosis of input stage

For diagnosis of the input stage, the calibration microcontroller calculates the expected

signal magnitude using the temperature information and the EEPROM constants and

compares it to the signal magnitude based on the current measurement.

If the difference of the two magnitudes is greater than an allowed deviation, an error

condition is signaled to the user.

The allowed difference depends on the bits DI1 to DI0 in the EEPROM control information

word.

Diagnosis of output stage

Both analog outputs are supervised by the auxiliary A/D-converter which reads the

present analog signal and converts it back to the digital domain with a resolution of 8 bits.

The digitized value is compared to the digital angle value originally sent.

If the difference of these two values is greater than an error bound, an error condition is

signaled by switching off the analog outputs.

The allowed difference depends on the bits DO1 to DO0 in the EEPROM control

information word.

CRC check of EEPROM constants

During normal operation mode a Cyclic Redundancy Codes (CRC) code of the

configuration constants taken from the EEPROM is calculated on a regular basis. This

code is compared to a pre-calculated CRC code from the EEPROM (CRC). If there is a

mismatch, an error condition is signaled to the user by setting the error flag in the digital

output word or by switching off the analog outputs.

The CRC code used is the CRC-16 code (ISO/IEC 3309:1993 and ITU-T V.42)

Watchdog timer

The KMA200 comprises a watchdog timer to supervise the flow of the program. After

reset, the watchdog is automatically activated. During operation the watchdog timer must

be toggled on a regular basis, as otherwise the error condition is signaled. The access to

the watchdog timer is protected against unwanted operations using a fail-safe watchdog

feed sequence.