Deserial – Serial Peripheral Interface (DSPI)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 30-31
30.4.1.5 Debug Mode
The debug mode is used for system development and debugging. If the MCU enters debug mode while the
FRZ bit in the DSPI_MCR is set, the DSPI stops all serial transfers and enters a stopped state. If the MCU
enters debug mode while the FRZ bit is negated, the DSPI behavior is unaffected and remains dictated by
the module-specific mode and configuration of the DSPI. The DSPI enters debug mode when a debug
request is asserted by an external controller. See Figure 30-19 for a state diagram.
30.4.2 Start and Stop of DSPI Transfers
The DSPI has two operating states: stopped and running. The states are independent of DSPI
configuration. The default state of the DSPI is stopped. In the stopped state, no serial transfers are initiated
in master mode and no transfers are responded to in slave mode. The stopped state is also a safe state for
writing the various configuration registers of the DSPI without causing undetermined results. The TXRXS
bit in the DSPI_SR is negated in this state. In the running state, serial transfers take place. The TXRXS bit
in the DSPI_SR is asserted in the running state. Figure 30-19 shows a state diagram of the start and stop
mechanism. The transitions are described in Table 30-24.
Figure 30-19. DSPI Start and Stop State Diagram
State transitions from running to stopped occur on the next frame boundary if a transfer is in progress, or
on the next system clock cycle if no transfers are in progress.
Table 30-24. State Transitions for Start and Stop of DSPI Transfers
Transition # Current State Next State Description
0 Reset Stopped Generic power-on-reset transition
1 Stopped Running The DSPI is started (DSPI transitions to running) when all of the following
conditions are true:
• EOQF bit is clear
• Debug mode is unselected or the FRZ bit is clear
• HALT bit is clear
2 Running Stopped The DSPI stops (transitions from running to stopped) after the current frame for
any one of the following conditions:
• EOQF bit is set
• Debug mode is selected and the FRZ bit is set
• HALT bit is set
Running
TXRXS = 1
Stopped
TXRXS = 0
Reset
Power-on-Reset 0
1
2
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