10. AFC Command

Configures automatic frequency control (AFC), which measures the transmitter and receiver frequency offset and can adjust the receiver frequency to compensate for it.

Register Fields

Bits

Name

Meaning

API

7:6

a1:a0

AFC operating mode

rfm12_set_afc_mode()

5:4

rl1:rl0

AFC range limit

rfm12_set_afc_range_limit()

3

st

Store-offset strobe

rfm12_set_afc_store_offset()

2

fi

Fine mode

rfm12_set_afc_fine_mode()

1

oe

Offset-register output enable

rfm12_set_afc_output_register_enable()

0

en

AFC calculation enable

rfm12_set_afc_enable()

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

Command Functions

rfm12_set_afc_mode()

RFM12_result_t rfm12_set_afc_mode(RFM12_t *dev, RFM12_afc_mode_t mode)

Stage the AFC automatic operating mode.

The following table maps the header’s enum names to the datasheet behavior of their encoded values.

Selection

a1:a0

Behavior

RFM12_AFC_MODE_OFF

00

Automatic operation off; the microcontroller controls the strobe.

RFM12_AFC_MODE_ON

01

Runs once after each power-up.

RFM12_AFC_MODE_ON_AFTER_RECEIVING

10

Retains the offset only during reception while VDI is high.

RFM12_AFC_MODE_KEEP_OFFSET_ON_RECEIVE

11

Retains the offset independently of the VDI signal.
Parameters:

  • dev – RFM12 radio instance.

  • mode – AFC operating mode selection.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_afc_range_limit()

RFM12_result_t rfm12_set_afc_range_limit(RFM12_t *dev, RFM12_afc_range_t range_limit)

Stage the allowed range of the AFC frequency-offset register.

Selection

Offset range in frequency steps

RFM12_AFC_RANGE_UNRESTRICTED

No range restriction

RFM12_AFC_RANGE_15_TO_16

-16 through +15

RFM12_AFC_RANGE_7_TO_8

-8 through +7

RFM12_AFC_RANGE_3_TO_4

-4 through +3

One frequency step is 2.5 kHz in the 433 MHz band, 5 kHz in the 868 MHz band, or 7.5 kHz in the 915 MHz band.

Parameters:

  • dev – RFM12 radio instance.

  • range_limit – AFC frequency-offset range selection.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_afc_store_offset()

RFM12_result_t rfm12_set_afc_store_offset(RFM12_t *dev, RFM12_enable_t enable)

Stage the store-offset strobe bit.

A rising edge on the hardware st bit stores the latest calculated frequency error in the AFC offset register. This setter stages the bit level; it does not immediately generate a strobe.

To generate another rising edge when st is already high, stage and apply the disabled setting, then stage and apply the enabled setting. Staging both levels before a single apply does not transmit both edges.

Parameters:

  • dev – RFM12 radio instance.

  • enable – Set or clear the store-offset strobe bit.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_afc_fine_mode()

RFM12_result_t rfm12_set_afc_fine_mode(RFM12_t *dev, RFM12_enable_t enable)

Stage the AFC fine-mode setting.

Fine mode approximately doubles the processing time and halves the measurement uncertainty compared with normal operation.

Parameters:

  • dev – RFM12 radio instance.

  • enable – Enable or disable high-accuracy AFC fine mode.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_afc_output_register_enable()

RFM12_result_t rfm12_set_afc_output_register_enable(RFM12_t *dev, RFM12_enable_t enable)

Stage the AFC offset-register output enable setting.

Enabling this setting allows the stored offset to be added to the PLL frequency control word. Offset calculation is controlled separately by rfm12_set_afc_enable().

Parameters:

  • dev – RFM12 radio instance.

  • enable – Enable or disable application of the stored frequency offset.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_set_afc_enable()

RFM12_result_t rfm12_set_afc_enable(RFM12_t *dev, RFM12_enable_t enable)

Stage the AFC frequency-offset calculation enable setting.

Applying the calculated offset to the PLL is controlled separately by rfm12_set_afc_output_register_enable().

Parameters:

  • dev – RFM12 radio instance.

  • enable – Enable or disable frequency-offset calculation by the AFC circuit.

Returns:

RFM12_OK on success, or an appropriate RFM12_result_t error.

rfm12_reset_afc()

RFM12_result_t rfm12_reset_afc(RFM12_t *dev)

Reset the staged AFC 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.