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# 1.2.6.4.11 SRV_USI_HANDLE_INVALID Macro

## C

    #define SRV_USI_HANDLE_INVALID  (((SRV_USI_HANDLE) -1))

## Summary

Definition of invalid USI handle.

## Description

This definition is used to indicate that an USI handle (SRV_USI_HANDLE Typedef) is invalid. SRV_USI_Open returns this value if:

- the specified instance has been already opened
- the instance being opened is not initialized or is invalid
- if there is an error opening the serial interface (USB CDC instances only)

## Remarks

The handle returned from SRV_USI_Open should be checked to ensure it is different to SRV_USI_HANDLE_INVALID before attempting to call any other USI routine using the handle.

Rev: G