STS1TX datasheet(22/70 Pages) STMICROELECTRONICS

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Operating modes

STS1TX

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DocID025109 Rev 1

Operating modes

The STS1TX is equipped with a built-in main controller which controls the switching

between the two main operating modes: transmit (TX).

In shutdown condition (the STS1TX can be switched on/off with the external pin SDN, all

other functions/registers/commands are available through the SPI interface and GPIOs), no

internal supply is generated (in order to minimize battery leakage), and hence, all stored

data and configurations are lost. The GPIO and SPI ports during SHUTDOWN are in HiZ.

From shutdown, the STS1TX can be switched on from the SDN pin and goes into READY

state, which is the default, where the reference signal from XO is available.

From READY state, the STS1TX can be moved to LOCK state to generate the high

precision LO signal and/or TX mode. At the end of the operations above, the STS1TX can

return to its default state (READY) and can then be put into a sleep condition (SLEEP state),

with very low power consumption. If no timeout is required, the STS1TX can be moved from

READY to STANDBY state, which has the lowest possible current consumption while

retaining FIFO, status and configuration registers. To manage the transitions towards and

between these operating modes, the controller works as a state-machine, whose state

switching is driven by SPI commands. See Figure 4 for state diagram and transition time

between states.

Figure 4. Diagram and transition

The STS1TX radio control has three stable states (READY, STANDBY, LOCK) which may

be defined stable, and they are accessed by the specific commands (respectively READY,

STANDBY, and LOCKTX), which can be left only if any other command is used. All other

states are transient, which means that in a typical configuration, the controller remains in

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