7.3.4 Cyclic Redundancy Check (CRC)

ISO1228 has a cyclic redundancy check that looks for errors in data communication across the isolation barrier.

Six-bit CRC is implemented internal to ISO1228. Detection of CRC error results in nFAULT flag being asserted.

The corresponding bit in the SPI register is also made high. In case of CRC error, the previous OUTx data is

retained till the next successful communication occurs across barrier.

7.3.5 FAULT Indication

ISO1228 monitors the following fault conditions: Power Loss Detection on the field side, Over Temperature

Detection and Thermal Shut Down on the field side, Wire-Break detection on any input channel, and CRC failure

in serial communication across the isolation barrier. Upon detection of any fault, the corresponding bit in the

SPI register is made high. Similarly, any fault detection will be flagged on the nFAULT pin (active low). Ignore

the nFAULT pin and the data in the SPI registers till 25ms after power up. The fault status in the SPI register

is maintained till the fault register is read, provided the underlying fault condition is resolved. nFAULT pin is

asserted for at least 9us or until the SPI fault register is read, whichever comes first, provided the underlying fault

condition is resolved. If Field Power Loss or CRC bit is set, other bits in the Fault register (02h) do not care.

7.3.6 Digital Low Pass Filter

The ISO1228 supports in-built digital low pass filters on the INx and WBx data paths. The filters can be

programmed through SPI registers (where each channel filter can be individually programmed) or through the

pins F0 and F1. F0 and F1 pins support three input states, high, low, and float, resulting in 9 values of digital

filtering. Refer to the Switching Characteristics section for values of the digital filters. The filter values in the SPI

registers take precedence. If any SPI filter Enable has a non-zero value, then the states of F0 and F1 pins are

ignored.

ISO1228 also supports a digital filter on the Wire Break detection fault. This is a fixed, non-programmable, 30ms

filter.

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ISO1228

SLLSFN5A – JUNE 2023 – REVISED FEBRUARY 2024

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