
MC68HC05F8
MOTOROLA
9-5
DTMF/MELODY GENERATOR
9
When one mode is selected, the pin associated with that mode will be activated, but the other pin
will remain at its idle state. The idle state for TONEOUT output pin is a tri-state, and TONEX output
pin is a logic high. The nal state of an active pin is dependent on the values of TGER, TGEC (see
Table 9-4), FCR and FCC bits (when illegal values is input).
When both MS1 and MS0 are set, the generator can generate both single tone melody at the
column path and ToneX at the row path simultaneously.
TGER, TGEC - Tone Generation Enable for Row and Column Paths
When both bits are held low, the DMG is disabled by forcing the two frequency counters and the
two PLA scanning counters to their reset states. The TONEOUT output is set to tri-state, the
TONEX output is set to logic low, and the active lter is turned off by shutting down all related
current sources to prevent DC power dissipation.
When a TGE bit for a path is held high (provided that the value in the frequency control register
for that path is legal, and the mode chosen is not ToneX mode) the generator is enabled. All the
counters associated with that path are then run from their reset states, and the active lter is
turned on to allow generated tone of that path to be output.
In DTMF dialling, the row and column tone values are rst entered to the FCR and FCC registers,
and then the TGER and TGEC bits are set or reset simultaneously to achieve dual tone multiple
frequency. Similarly, in melody generation, one path is chosen as the high part, and the other, the
low part. The TGER and TGEC bits are then set and reset according to the rhythm required by the
musical tune. Of course, one can exhibits only single tone melody by disabling either TGER or
TGEC permanently. The DTMF column and row frequency tones can also be output separately
for testing by enabling just the one path.
Table 9-3 DMG Operating Modes
MS1
MS0
Mode
TONEOUT output
TONEX output
0
Sine Wave
DTMF/Melody
High
0
1
Square Wave
Melody
High
1
0
ToneX
tri-state
ToneX
1
Square Wave+ToneX
Monotonic Melody
ToneX
Table 9-4 Effect of Tone Generation Enable on DMG
TGER
TGEC
Row Path
Column Path
Filter
Tone
0
Off
Silent
0
1
Off
Active
Single
1
0
Active
Off
Active*
Single
1
Active
Dual*
* In ToneX mode, the lter is off and only single tone can be generated.
TPG
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