Chapter 24 Cross Triggering Unit (CTU)
MPC5602P Microcontroller Reference Manual, Rev. 4
620
Freescale Semiconductor
24.6
Power safety mode
To reduce power consumption two mechanisms are implemented:
•
MDIS bit in the CTUPCR
•
STOP mode
24.6.1
MDIS bit
The MDIS bit in the CTUPCR is used for stopping the clock to all non memory mapped registers.
24.6.2
STOP mode
To reduce consumption, it is also possible to enable a stop request from the Mode Entry module.
The
FIFOs are considered a lot like memory mapped registers, otherwise there could be some problems if a
read operation occurs during the MDIS bit set period. When the clock is started after an MDIS bit setting
or a stop signal, some mistakes could occur. For example, a wrong trigger could be provided because it
was programmed before the stop signal was performed, and some incorrect write operations into the FIFOs
could happen. For this reason after a stop signal after a MDIS bit setting the FIFO have to be empty. In
order to avoid the problems linked to a wrong trigger, the CTU output can be disabled by the CTU_ODIS
bit
and the ADC interface state machine can be reset by the CRU_ADC_R (see
triggering unit control register (CTUCR)
24.7
Interrupts and DMA requests
24.7.1
DMA support
The DMA can be used to configure the CTU registers. One DMA channel is reserved for performing a
block transfer, and the MRS can be used as an optional DMA request signal (MRS_DMAE bit in the CTU
Interrupt/DMA Register).
NOTE
If enabled, the DMA request on the MRS occurrence is performed only if a
reload is performed, that is, only if the GRE bit is set.
Moreover, this CTU implementation requires DMA support for reading the data from the FIFOs. One
DMA channel is available for each FIFO. Each FIFO can perform a DMA request when the number of
words stored in the FIFO reaches the threshold value.
24.7.2
CTU faults and errors
Faults and errors that could occur during the programming include:
•
An MRS occurs while user is updating the double-buffered registers and the MRS_RE bit is set.
•
Receiving more than eight EVs before that the next MRS occurs in TGS sequential mode and the
SM_TO bit is set.