6. Data Filter Command

Configures clock recovery, data filtering, and the Data Quality Detector (DQD) threshold.

Register Fields

Bits	Name	Meaning	API
7	al	Automatic clock-recovery mode	rfm12_set_clock_recovery_mode()
6	ml	Manual clock-recovery speed	rfm12_set_clock_recovery_speed()
5	Fixed	Must be 1	None
4	s	Filter type	rfm12_set_filter_type()
3	Fixed	Must be 1	None
2:0	f2:f0	Data Quality Detector threshold	rfm12_set_dqd_threshold()

The setters listed in the register field table above directly configure fields in the Data Filter Command. The setters and reset function update staged configuration without communicating with the radio. Use rfm12_apply_to_radio() to write the staged settings.

Data Types

RFM12_clock_recovery_mode_t

type RFM12_clock_recovery_mode_t

Enum. Automatic or manual clock recovery selection for bit 7.

Constant	Value	Meaning
RFM12_CLOCK_RECOVERY_MANUAL	0	Manual speed selection.
RFM12_CLOCK_RECOVERY_AUTO	1	Automatic clock recovery.

RFM12_clock_recovery_speed_t

type RFM12_clock_recovery_speed_t

Enum. Manual clock recovery speed for bit 6. Used only with RFM12_CLOCK_RECOVERY_MANUAL.

Constant	Value	Meaning
RFM12_CLOCK_RECOVERY_SLOW	0	Slow recovery.
RFM12_CLOCK_RECOVERY_FAST	1	Fast recovery.

RFM12_filter_type_t

type RFM12_filter_type_t

Enum. Receive data filter selection for bit 4.

Constant	Value	Meaning
RFM12_FILTER_DIGITAL	0	Digital filter.
RFM12_FILTER_ANALOG_RC	1	Analog RC filter.

RFM12_dqd_threshold_t

type RFM12_dqd_threshold_t

Enum. Data Quality Detector threshold for bits 2:0. Hardware supports 0 through 7; the recommended operating range is 5 through 7.

Constant	Value	Meaning
RFM12_DQD_THRESHOLD_0	0	Threshold 0.
RFM12_DQD_THRESHOLD_1	1	Threshold 1.
RFM12_DQD_THRESHOLD_2	2	Threshold 2.
RFM12_DQD_THRESHOLD_3	3	Threshold 3.
RFM12_DQD_THRESHOLD_4	4	Threshold 4.
RFM12_DQD_THRESHOLD_5	5	Threshold 5.
RFM12_DQD_THRESHOLD_6	6	Threshold 6.
RFM12_DQD_THRESHOLD_7	7	Threshold 7.

Command Functions

rfm12_set_clock_recovery_mode()

RFM12_result_t rfm12_set_clock_recovery_mode(RFM12_t *dev, RFM12_clock_recovery_mode_t mode)

Stage the clock-recovery mode.

Select RFM12_CLOCK_RECOVERY_AUTO to start clock recovery in fast mode and switch to slow mode after locking. In automatic mode, the manual speed setting has no effect.

Select RFM12_CLOCK_RECOVERY_MANUAL to use the speed selected by rfm12_set_clock_recovery_speed().

Parameters:

• dev – RFM12 radio instance.

• mode – Automatic or manual clock-recovery mode.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_clock_recovery_speed()

RFM12_result_t rfm12_set_clock_recovery_speed(RFM12_t *dev, RFM12_clock_recovery_speed_t speed)

Stage the manual clock-recovery speed.

Select RFM12_CLOCK_RECOVERY_FAST for fast attack and release, or RFM12_CLOCK_RECOVERY_SLOW for slow attack and release. This setting takes effect only when clock recovery is in manual mode.

The datasheet recommends a 4- to 8-bit alternating preamble for fast mode and a 12- to 16-bit preamble for slow mode. Slow mode requires more accurate bit timing.

Parameters:

• dev – RFM12 radio instance.

• speed – Manual clock-recovery speed selection.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_filter_type()

RFM12_result_t rfm12_set_filter_type(RFM12_t *dev, RFM12_filter_type_t filter_type)

Stage the data-filter type.

Select RFM12_FILTER_DIGITAL for the digital filter, whose time constant is automatically adjusted to the data rate configured by rfm12_set_data_rate().

Select RFM12_FILTER_ANALOG_RC for the analog RC filter. This mode requires an external capacitor between pin 7 and VSS to set the filter cutoff frequency. The internal clock-recovery circuit and FIFO cannot be used with the analog RC filter.

Parameters:

• dev – RFM12 radio instance.

• filter_type – Digital or analog RC filter selection.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_dqd_threshold()

RFM12_result_t rfm12_set_dqd_threshold(RFM12_t *dev, RFM12_dqd_threshold_t threshold)

Stage the Data Quality Detector threshold.

The hardware supports thresholds 0 through 7, selected using RFM12_DQD_THRESHOLD_0 through RFM12_DQD_THRESHOLD_7. The datasheet recommends thresholds 5 through 7; lower thresholds can cause noise to be treated as a valid FSK signal.

Parameters:

• dev – RFM12 radio instance.

• threshold – Data Quality Detector threshold selection.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_reset_data_filter()

RFM12_result_t rfm12_reset_data_filter(RFM12_t *dev)

Reset the staged Data Filter Command values to their defaults.

This function does not communicate with the radio. The changed settings are written to the radio by rfm12_apply_to_radio().

Parameters:

• dev – RFM12 radio instance.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.