# cdiStartSignalDetector

Starts on-board monitoring of the signaling bits. You must issue cdiEnableBattery before you start cdiStartSignalDetector.

#### Prototype

DWORD cdiStartSignalDetector ( CTAHD ctahd, CDI_SIGNALDETECTOR_PARMS *parms)

Argument | Description
ctahd | Context handle.
parms | Pointer to a structure specifying signal detection parameters: typedef struct { DWORD size; DWORD timeon; DWORD timeoff; DWORD min_flash_hook; DWORD max_flash_hook; } CDI_SIGNALDETECTOR_PARMS Refer to CDI_SIGNALDETECTOR_PARMS for field descriptions.

#### Return values

Return value | Description
SUCCESS |
CTAERR_BAD_ARGUMENT | Argument is not in the valid range.
CTAERR_INVALID_CTAHD | Handle is invalid.

#### Events

Event | Description
CDIEVN_OFF_HOOK | Station picked up.
CDIEVN_ON_HOOK | Station hung up.
CDIEVN_FLASH_HOOK | Flash-hook generated.
CDIEVN_A_CHANGE_ON | A bit was just set.
CDIEVN_A_CHANGE_OFF | A bit was just reset.

#### Details

Once station power is enabled, the DSP can monitor signaling bits. Use cdiStartSignalDetector to start on-board monitoring of the signaling bits.

When operating in enhanced mode, the DSP qualifies bit changes according to the parameters in the CDI_SIGNALDETECTOR_PARMS structure, as described in the following table:

Bit state change | Event presented to application
--- | ---
Qualified on-hook to off-hook (more than the timeon field value). | CDIEVN_OFF_HOOK
All off-hook to on-hook transitions less than min_flash_hook are ignored. | No events
Qualified off-hook to on-hook (more than min_flash_hook field value and remains on for less than the max_flash_hook field value). | CDIEVN_FLASH_HOOK
Qualified off-hook to on-hook (more than the max_flash_hook field value). | CDIEVN_ON_HOOK

When operating with enhanced mode disabled, only low-level supervisory signaling events CDIEVN_A_CHANGE_ON and CDIEVN_A_CHANGE_OFF are presented. Flash-hook detection is disabled.

Refer to Monitoring signaling bits for more information about signal detection.

#### See also

cdiStopSignalDetector