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TC1796
System Units (Vol. 1 of 2)
System Control Unit
User’s Manual
5-6
V2.0, 2007-07
SCU, V2.0
5.1.3.2
Sleep Mode
The Idle Mode is requested by software when writing to register PMG_CSR with bit field
REQSLP = 10
B
.
Entering Sleep Mode
Sleep Mode is entered in two steps:
1. The CPU is put into Idle Mode as described in the previous section. When the PMSM
receives the Idle acknowledge signal back from the CPU, it proceeds with the second
step.
2. A sleep signal is broadcasted on the FPI Bus. Each FPI Bus interface unit receives
this signal. The response of each FPI Bus unit to the sleep signal is determined by
its clock control register. These clock control registers must have been previously
configured by software.
TC1796 State During Sleep Mode
Sleep Mode is disabled for a unit if its clock control register bit EDIS is set to 1. The sleep
signal is ignored in this case and the corresponding unit continues normal operation. If
EDIS = 0, Sleep Mode is enabled for this unit and the sleep signal will cause this unit to
enter Sleep Mode. Two actions then occur:
•
The unit’s bus interface finishes whatever transaction was in progress when the
signal was received.
•
The unit’s functions are suspended.
The TriCore architecture qualifies the actions in step 2 as follows. Depending on the
module’s clock control register Fast Shut-Off Enable bit, FSOE, the module’s clocks are
either immediately stopped (FSOE = 1), or the unit is allowed to finish ongoing
operations (FSOE = 0) before the clocks are stopped. For example, setting FSOE to 1
for a serial port will stop all actions in the serial port immediately when the sleep signal
is received. Ongoing transmissions or receptions will be aborted. If FSOE is 0, ongoing
transmissions or receptions will be completed, and then the clock will be shut off. The
purpose of setting FSOE = 1 is to allow a debugger to observe the internal state of a
peripheral unit immediately.
Exiting Sleep Mode
The system will be returned to Run Mode by the same events that exit Idle Mode. The
response of the CPU to being awakened is also the same as for Idle Mode. Peripheral
units that have entered Sleep Mode will switch back to their selected Run Mode
operation.