MPC563XM Reference Manual, Rev. 1
822
Freescale Semiconductor
Preliminary—Subject to Change Without Notice
23.4.5.4.2
Channel Modes Overview
Predefined channel modes are divided according to the way they treat transitions in two basic modes:
•
Single Transition Modes
(mnemonic suffix
_st
): in these modes the first transition (flagged in
TDL1) issues a service request, and captures both time bases (selected by TBS1[1] and TBS2[1])
except on sm_st_e. The second transition (flagged in TDL2) does not issue a service request, but
it captures time base selected by TBS2[1], except on sm_st_e.
•
Double Transition Modes
(mnemonic suffix
_dt
): in these modes the second transition (flagged
in TDL2) issues a service request, and each transition captures its own selected time base
(Transition 1 and Transition 2 capture time bases selected by TBS1[1] and TBS2[1], respectively).
In predefined modes, Transition 2 is always (but not only) enabled by Transition 1, so that transitions are
always ordered: TDL1 is set on the first transition and TDL2 on the second. Unordered transitions are
possible with user-defined mode, when UDCM bit T1ET2=0. Matches are generally not ordered, except
on specific ordered match modes m2_o_st and m2_o_dt. Match capture(s) never overrides a Transition
capture, while Transition captures can always override a Match capture, either in predefined or
user-defined modes.
The following general rules apply to both predefined and user-defined modes:
•
Blocking of one Match by the other, when it occurs, is done through MRLEs.
•
Matches always block themselves by resetting their own MRLEs (Match 1 always blocks Match
1, Match 2 always blocks Match2).
Predefined modes differ mostly by the way matches affects and are affected by other matches and
transitions, as explained in next sections. However, some general rules on Match blocking apply:
•
Match 2 is blocked by first transition (TDL1) in single transition modes, and by second transition
(TDL2) in double transition modes.
•
Both Matches are blocked by first transition in single transition modes.
NOTE
The rules above and in following sections may be overruled by the state of
the channel latches if they are set/reset by microcode or if channel mode is
changed. Care must be taken to change channel modes, and is advisable to
reset channel flags MRL1/2, TDL1/2 and MRLE1/2 before writing PDCM,
or to UDCM when user-defined mode is selected.
Either Match, Blocking Modes (em_b_st, em_b_dt)
In these modes the first match recognition that occurs blocks the other match recognition and generates a
service request. They end up with one service request for two programmed match recognitions where only
the first match recognition has an actual effect. If both match recognitions occur at the same time, both
MRL1 and MRL2 are set, before the mutual blocking takes effect.