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Development Trigger Semaphore (DTS)
It is the user's responsibility to ensure that the tool has time to retrieve the
data prior to that particular trigger being set a second time. It is also
permissible to have multiple triggers active at the same time or for a second
trigger to be set before a previous trigger has been serviced, as long as it is
not the same trigger (unless it is acceptable to the tool to not receive every
data set).
Figure 38-7
shows an example DTS startup sequence for an external real-time data acquisition system. The
startup and synchronization sequence can be as simple or as complicated as the need requires. However, a
typical startup sequence is as follows:
1. The DTS_STARTUP register is cleared by a power on reset or any CPU reset.
2. The tool writes a non-zero value to the DTS_STARTUP register.
3. The CPU (user application software) then reads the value of the DTS_STARTUP register. Based
on this value, different initialization options can be selected. The bits can be used for any
application specific definitions.
4. Since the DTS_SEMAPHORE register is cleared when the tool reads the current value. The tool
should perform all necessary initialization before reading this register. The application software
can then check that the DTS_SEMAPHORE register was cleared by the tool, to determine that it
is safe to start using it for its intended raster trigger semaphore function.
5. An optional hand shake from the CPU can be used to inform the tool that the user software has
detected that the tool is attached and the CPU has performed the proper initialization for the tool
by writing a predefined value to the DTS_SEMAPHORE register (the example shown in the figure
above uses 0xAAAA_AAAA—all A's was used since it is unrealistic that 16 channels could be
enabled very quickly after start up after a reset).
1700
NOTE
Figure 38-7. DTS startup sequence example
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor
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