3.9.1 Overview

The sequencer state machine implements major control parts to set up and run the receive and transmit operations. It makes the start-up and shutdown process more robust and predictable because it is not susceptible to timing deviations as if controlled by the AVR core with a varying workload.

To set up a reception or transmission chain, the software initially needs to load the configuration, such as the filter settings and frequency parameters to the corresponding hardware registers. Afterward, it hands over the control to the SSM that enables all required blocks with an appropriate timing, taking into account the settling times of filters and analog components.

The configuration of the SSM offers some flexibility such as deciding whether VCO tuning is needed or not. The start-up flows are broken up into smaller elements, allowing parts of the sequencer state machine functionality to be used only. In addition, the start-up flows augment software-controlled sequences.

The integrated dedicated VCO tuning timer frees other on-chip resources for application use.

The following figure shows a diagram of useful sub-state-machine sequences. The system needs to be in the IDLEMode(XTO) with the RF front end powered up and the system running on clkXTO.

Several state machines are needed to transition between the three shown states of IDLEMode(XTO), RXMode and TXMode. The flow may be interrupted between every sub-state machine to intersperse some user software code. Other orders of sub-state machines than those shown in the diagram are prohibited.
Figure 3-37. SSM Sub-State-Machine Sequence Diagram

The following figure shows the standard sequence for initializing the system for RF reception. The optional VCO tuning sub-state machine is marked in light gray.

Figure 3-38. SSM Start RX Sequence

The following figure shows the standard sequence for initializing the system for transmission. Here the VCO tuning and the antenna tuning sub-state machines are optional.

Figure 3-39. SSM Start TX Sequence

The following figure shows the standard sequences for direct switching. VCO tuning is required as described below for the RX to TX switching and starting the TX sequence. The antenna tuning sub-state machine is optional.

For TX to RX switching the VCO tuning sub-state machine is required if one of the following conditions is true:

  • The ambient temperature changes by more than 40K
  • The VCO frequency changes by more than 25 MHz
Figure 3-40. SSM RX to TX Switching Sequence
The following figure shows the standard sequences for direct switching.
Figure 3-41. SSM TX to RX Switching Sequence

When the RF channel is switched during reception, it needs to be ensured that the PLL has settled to the new frequency. A new PLL lock sequence is thus required if one of the following conditions is true:

  • A VCO tuning occurred
  • High-Band/Low-Band switching (FECR.LBNHB modification)
  • Modification of the FEMS.PLLM or FEMS.PLLS values
  • Modification of the MSB in the FFREQ1H or FFREQ2H register
  • Modification of the PLL frequency by more than 1 MHz

The RX to RX switching sequence is realized as shown in the following figure. Once the RX DSP is stopped, the PLL lock sub-state machine waits for the lock signal of the PLL and the RX DSP is enabled again while running on the new frequency.

The same applies for TX frequency switching, as shown in the Figure 3-43.

Figure 3-42. SSM RX to RX Switching Sequence
Figure 3-43. SSM TX to TX Switching Sequence

The SSM must be activated in the corresponding power reduction register PRR2.PRSSM (see Sleep Modes and Active Power Reduction).