18.2.2 Control Signals

Start-up signal, USS_PWRREQ

USS_PWRREQ = 0 → 1 is the signal that powers up the USS module and starts a new measurement. If the USS module is already powered up, then the PSQ initiates a new measurement immediately. UUPSCTL.USSPWRUPSEL determines the source of the USS_PWRREQ signal. When the PSQ detects USS_PWRREQ signal, no additional event is accepted by the PSQ until the measurement is complete. UUPSCTL.USS_BUSY indicates whether or not the USS module is in a power transition or performing a measurement. While UUPSCTL.USS_BUSY = 1, the PSQ ignores the USS_PWRREQ signal (0 → 1).

Reset and Low Power Bias Mode control signals

On device Power Up the all USS submodules are kept in reset state. Set UUPSCTL.SWRST = 0 to release reset and put the module into operation mode.

The operation mode has to be selected before the USS is powered up. For Auto mode and Register Mode set SAPGMCNF.LPBE=0.

To select Low Power Bias Mode set SAPHMCNF.LPBE=1. SAPHMCNF.LPBE shall only be changed while the PSQ is in OFF state.

• USS_SWRST: SW reset signal fo all USS submodules.
• ASQ_LPBE: Enables Low Power Bias operation mode here the ASQ takes has full control over the input multiplexer and channel selection.

Power-up control signals

When USS_PWRREQ = 0 → 1 is detected, the PSQ starts the power-up sequence if the USS module has not been powered up (UUPSCTL.UPSTATE = 0). The PSQ requests the required reference voltage and currents, then enables the USS LDO and enables HSPLL. When the PLL is locked, generate the PSQ_START signal to ASQ.

• PSQ_SREFREQ: Request signal to the share reference module.
• PSQ_LDOUP: Enables the USS LDO after the reference voltage and currents from BIAS_REF module are settled.
• PSQ_PLLUP: Enables HSPLL when UUPSCTL.LDORDY = 1.
• PSQ_START: PSQ to ASQ to start a new measurement sequence. The PSQ asserts the signal when IREF_MOD, USS LDO, and HSPLL are fully settled and UUPSCTL.ASQEN bit = 1.
• PSQ_STOP: PSQ to ASQ to stop the existing measurement immediately. The PSQ asserts the signal when UUPSCTL.USSPWRDN = 1 or UUPSCTL.USSSTOP = 1.

Measurement control signals

When USS_START = 0 → 1 is detected, the ASQ starts a new measurement sequence based on the timing information in the time mark registers (SAPHATM_A to SAPHATM_F).

• ASQ_PPGTRG: ASQ to PPG to generate excitation pules.
• ASQ_ACQARM: ASQ to SDHS to power up the SDHS module.
• ASQ_ACQTRG: ASQ to SDHS to start data conversion and transfer output data to target memory.
• SHDS_ACQDONE: SDHS to ASQ to acknowledge that the preconfigured sample size has been captured.

Power-down control states and signals

When the desired measurement sequences finish execution, the power-down process starts. There are three power states that can be chosen:

• READY: The USS module is fully powered up (no changes in power state).
• STANDBY: The USS module is powered off, but required reference voltage is kept on for faster wakeup.
• OFF: The USS module is fully powered off.

The ASQ asserts ASQ_ACQDONE to acknowledge the PSQ that the measurement is compete. Depending on the selected power state, ASQ_PDREQ or ASQ_STBYREQ can be asserted along with the ASQ_ACQDONE signal.

• ASQ_PDREQ: Goes to OFF state.
• ASQ_STDBYREQ: Goes to STANDBY state.
• ASQ_ASQDONE: Indicates that the measurement is complete. If neither ASQ_PDREQ nor ASQ_STDBYREQ is asserted, then stay in READY state.

Emergency measurement stop control signals

While the USS module is active, the current measurement sequence can be stopped at any time:

• PSQ_STOP: PSQ to ASQ to stop the current measurement immediately (when UUPSCTL.USSSTOP = 1 or UUPSCTL.USSPWRDN = 1).
• ASQ_PPGSTOP: ASQ to PPG to stop pulse generation if the PPG is active.
• ASQ_SDHSSTOP: ASQ to SDHS to stop the data conversion and turn off the SDHS if the SDHS is active.