Philips CEM2100/00, Service Manual

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8.3.6 Programmable Pulse Generate (PPG) Output Mode
In the programmable pulse generation (PPG) mode, an arbitrary duty pulse is generated by counting per-
formed in the internal clock. To start the timer, TC1CR<TC1S> specifies either the edge of the input pulse to
the TC1 pin or the command start. TC1CR<MPPG1> specifies whether a duty pulse is produced continuously
or not (one-shot pulse).
• When TC1CR<MPPG1> is set to “0” (Continuous pulse generation)
When a match between the up-counter and the TC1DRB value is detected after the timer starts, the
level of the
PPG
pin is inverted and an INTTC1 interrupt request is generated. The up-counter contin-
ues counting. When a match between the up-counter and the TC1DRA value is detected, the level of
the
PPG
pin is inverted and an INTTC1 interrupt request is generated. The up-counter is cleared at
this time, and then continues counting and pulse generation.
When TC1S is cleared to “00” during PPG output, the
PPG
pin retains the level immediately before
the counter stops.
• When TC1CR<MPPG1> is set to “1” (One-shot pulse generation)
When a match between the up-counter and the TC1DRB value is detected after the timer starts, the
level of the
PPG
pin is inverted and an INTTC1 interrupt request is generated. The up-counter contin-
ues counting. When a match between the up-counter and the TC1DRA value is detected, the level of
the
PPG
pin is inverted and an INTTC1 interrupt request is generated. TC1CR<TC1S> is cleared to
“00” automatically at this time, and the timer stops. The pulse generated by PPG retains the same
level as that when the timer stops.
Since the output level of the
PPG
pin can be set with TC1CR<TFF1> when the timer starts, a positive or neg-
ative pulse can be generated. Since the inverted level of the timer F/F1 output level is output to the
PPG
pin,
specify TC1CR<TFF1> to “0” to set the high level to the
PPG
pin, and “1” to set the low level to the
PPG
pin.
Upon reset, the timer F/F1 is initialized to “0”.
Note 1: To change TC1DRA or TC1DRB during a run of the timer, set a value sufficiently larger than the count value
of the counter. Setting a value smaller than the count value of the counter during a run of the timer may
generate a pulse different from that specified.
Note 2: Do not change TC1CR<TFF1> during a run of the timer. TC1CR<TFF1> can be set correctly only at initial-
ization (after reset). When the timer stops during PPG, TC1CR<TFF1> can not be set correctly from this
point onward if the PPG output has the level which is inverted of the level when the timer starts. (Setting
TC1CR<TFF1> specifies the timer F/F1 to the level inverted of the programmed value.) Therefore, the
timer F/F1 needs to be initialized to ensure an arbitrary level of the PPG output. To initialize the timer F/F1,
change TC1CR<TC1M> to the timer mode (it is not required to start the timer mode), and then set the PPG
mode. Set TC1CR<TFF1> at this time.
Note 3: In the PPG mode, the following relationship must be satisfied.
TC1DRA > TC1DRB
Note 4: Set TC1DRB after changing the mode of TC1M to the PPG mode.