Function

•     Check currently incoming RF signal strength and preamble quality

•     Specify the level of RSSI for subsequent receipts in LP and XLP modes

Purpose

•     Incoming RF signal strength and quality detection

•     Set filter level for incoming LP and XLP packets

Syntax

bit checkRF(uns8 level)

Parameters

level = RSSI_FILTER (0 to 64)

Values > 64 are not intended for signal filtration, but for special purposes. See getRSSI Preconditions for example.

Input values

bit _checkRFcfg_PQT     Preamble quality check enable in STD RX

•     0: RF carrier strength is checked (Default)

•     1: RF carrier strength and preamble quality are checked

This bit applies in STD RX mode only. In LP or XLP RX modes the preamble quality is always checked.

Return value

•     1: If _checkRFcfg_PQT = 0 in STD RX mode: Signal with specified level or higher detected

                                   (RSSI >= RSSI_FILTER)

If _checkRFcfg_PQT = 1 or in LP or XLP RX mode:

Signal with specified level or higher detected (RSSI >= RSSI_FILTER) and correct format of packet preamble is detected

•     0: Otherwise

Output values

•     Filter for all subsequent incoming LP and XLP packets is set to specified method and level

•     After checkRF finishing, RF IC stays always in RF Ready mode.

Preconditions

In LP and XLP RX modes, checkRF should be used only once whenever a change of filter level is needed. It should not be used repeatedly in the RX loop.

Remarks

•     Higher filtration brings higher immunity against noise and interferences but allows a lower range. See TR datasheet, table Relative RF range vs. checkRF(level).

•     checkRF(5) is recommended for immunity against weak noise.

•     Checking takes about 1 ms (when _checkRFcfg_PQT=0) or 2.8 ms (when _checkRFcfgPQT=1).

•     If _checkRFcfgPQT=1 and a packet transmitted in LP or XLP TX mode should be received in STD RX mode, toutRF ≥ 5 or 100, respectively, must be set.

•     Unlike getRSSI and RFRXpacket, checkRF does not update the lastRSSI register.

•     For reading out the RSSI value the getRSSI function is intended. See getRSSI Example.

Side effects

  –

See also

RFRXpacket, getRSSI

Example 1

              // Fast response receiving in STD mode

_checkRFcfg_PQT = 1;  // Check RF signal for preamble quality as well

if (checkRF(5))       // Detect signal with RSSI >= selected level

{

  if (RFRXpacket())   // Duration according to toutRF only if packet is sent.

  {                   // toutRF can be optimized for expected packet length.

    ...     

  }

}               // Otherwise only ~2.8 ms (or 1 ms if _checkRFcfg_PQT = 0) is spent.

... time-critical section can be placed here

Example 2

if (checkRF(10))    // Detect signal with RSSI >= selected level

   ...

Example 3

              // LP TX packet received in STD RX

_checkRFcfg_PQT = 1;       // Check RF signal for preamble quality as well

setRFmode(_RX_STD | _WPE); // Standard RX

toutRF = 5;                 // 5 or more is required, see Remarks

                            // Change 5 to 100 if XLP packet is expected

if (checkRF(5))             // Detect signal with RSSI >= selected level

{

  if (RFRXpacket())         // Duration according to toutRF only if packet is sent.

    ...     

Example 4

              // RF signal strength analyzer

while (1)
  if (checkRF(5)) pulseLEDR(); // LED flash if RSSI >= selected level detected