MPC563XM Reference Manual, Rev. 1
830
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
In single transition modes, TDL1 assertion may capture both time bases at once, while in double transition
modes each transition captures its related time base in its related capture register.
Double transition is always ordered, i.e TDL2 is enabled by TDL1 and generates the service request.
The channel logic supports various input modes with combinations of single/double transition and
single/double match, explained in the following subsections.
Either Match, Blocking, Single Transition (em_b_st)
On an input signal, this mode provides double timeout mechanism on a programmed transition edge with
two timebases. The signal transition blocks both pending matches, indicating that no timeout condition
occurred. The two match recognitions block each other, giving good separation in the entry table as to
which match recognition caused the first timeout condition, and generating only one service request. Either
match performs timebase captures which do not overwrite captures by transitions.
Either Match, Blocking, Double Transition (em_b_dt)
In double transition mode each transition is related to one match recognition. TDL1 assertion captures its
related timebase, blocks match1 and enables TDL2. TDL2 assertion blocks match2, captures its related
timebase and generates a service request. Match recognitions block each other, so if there is a match
timeout condition on TDL1, only one match service request is generated. This mode is good for qualifying
two signal transitions by match timeout mechanisms, with one service request. Note that although TDL1
assertion does not block Match2 recognition, the value captured in Capture1 by TDL1 assertion is not
overwritten by this recognition. The second transition blocks match2. Either match performs timebase
captures which do not overwrite captures by transitions.
Either Match, Non Blocking, Single Transition (em_nb_st)
On an input signal, this is a double timeout mechanism of independent match recognitions of two different
timebases. The match recognitions do not block each other, such that the microcode can check if one or
two match recognitions occurred before their related signal transition. The signal transition detection (by
IPAC1) asserts TDL1, blocks both matches, captures both time bases and generates a transition service
request, indicating that none of the two timeout conditions occurred. Any combination can be easily
resolved by microcode (for example, signal transition after Match1 and before Match2, or signal transition
after both Match1 and Match2).
Another possible use of this mode is allocating one match recognition for transition timeout and the other
for another non-critical timed task, adding functionality to a single channel. Since the transition detection
blocks both match recognitions, the match recognition of the other timed task is based on the fact that the
comparator checks greater-equal conditions. It may be delayed if it occurs in the period between the signal
transition detection (which blocks it) and the time TDL1 is negated by microcode. If matches are enabled
during the service, the same code can check if the match recognition of the timed task occurred in this
period, by negating TDL1 and writing to the CHAN register its own value (in order to update the MRL1
flag in the branch logic).