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Reaction Module (REACM)
MPC5644A Microcontroller Reference Manual, Rev. 6
720
Freescale Semiconductor
Figure 23-20. Modulation control word bank interfaces
23.4.3
Shared timer bank
The Shared Timer bank is an innovative concept of dynamic timer allocation. Since the number of timers
can be smaller than the number of channels in the Reaction Module, there is a possibility that all timers
are allocated at a certain time. This architecture is based on the low probability of such scenario since the
timer allocation is a sporadic event. The timers in the Shared Timer Bank are usually in IDLE state until
they are allocated by a channel. Any timer can be allocated as soon as it is IDLE. The shared timers work
in conjunction with a timer bank which stores values to be used by the timing measurement.
The Shared Timer Bank block is composed of two submodules:
•
Three 16-bit counters
•
A bank with maximum of 16 selectable 16-bit time values
If there is an attempt to allocate more than three timers then an error flag TAER (see
and no timer is allocated by the requesting channel. As a general guideline the system should be
dimensioned in such a way that the timer allocation is always possible.
NOTE
In case of an allocation error the channel forces DOFF to its output pin
preventing any damage to occur to the actuator being controlled. This state
will not change until bit TAER is cleared.
During the timer allocation the channel also provides the TIMERPT pointer which selects a timing value.
The valued pointed by TIMERPT is loaded into one of the three counters which counts down until reaching
zero. At this time a timeout indication is sent to the requesting channel and the timer is deallocate, moving
back to IDLE state.
REQUEST
SEL
ARBITER/
Request[15:1]
Modulation addr
Modulation
LOOP IOSS
TIMERPT
HDOFFPT
THRESPT
CPU
Control
Word Bank
Channel
Reaction
Access granted
Request
other
channels
SM
MM
HOD LOD
addr for the
Threshold Bank
addr for the
Timer Bank
addr for the
Hold-off Bank
sel addr
Holdoff
Bank
Modulation Word
CH0
Modulation information
Timer
Summary of Contents for MPC5644A
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