CLKM Frequency Change

This section describes, how the frequency of the CLKM signal is controlled. The CLKM signal is available at pin TRX_PIN_CLKM in all states except SLEEP, RX_ON_NOCLK, RX_AACK_ON_NOCLK, BUSY_RX_AACK_NOCLK. The frequency of the CLKM signal can be modified in two ways. The sequence PHY_CHANGE_CLKM_FAST can be used, if a clock change can happen on the fly, e.g. if a GPIO or a timer input is driven. If the CLKM signal is used as clock source for the MCU and therefore no on the fly frequency change is allowed, the sequence PHY_CHANGE_CLKM_SAFE is used doing a clock change using a wake-sleep-wake transition.

Parameters:
clkrate The clock rate parameter gives the frequency value for the CLKM signal, which can be one of the following values.
  • 0 : OFF, CLKM = LOW.
  • 1 : 1 MHz
  • 2 : 2 MHz
  • 3 : 4 MHz
  • 4 : 8 MHz
  • 5 : 16 MHz
The following sequences are defined:


PHY_CHANGE_CLKM_FAST

inline_mscgraph_63
Code example

PHY_CHANGE_CLKM_SAFE

Note:
The prep_clkchange() function is MCU dependent and is responsible to bring the MCU to a state, where a clock change is allowed. After asserting TRX_PIN_SLP_TR = HIGH the CLKM signal delivers 35 cycles before it is turned off (see also PHY_STATE_TRX_OFF__SLEEP).
inline_mscgraph_64
Code example

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