EM6621
7. Melody, Buzzer
A normal application is to drive a buzzer connected onto the terminal Buzzer.
This peripheral cell is a combination of a 7 frequency tone generator and a 4-bit timer, used to provide a 50%
duty cycle signal on the Buzzer terminal of a pre-selected length and frequency. The Buzzer terminal is active as
long as the timer is not 0 or the
SwBuzzer
is set to ‘1’. The 4-bit timer can be used for another application
independent of the Buzzer terminal by selecting "silence" instead of another frequency on the Buzzer output.
"Silence" can also be used as part of a melody, or to switch off the buzzer.
To use the buzzer independent of the 4-bit timer one has to set the switch
SwBuzzer.
This bit is in register
RegMelTim
and selects the signal duration on the buzzer output. If
SwBuzzer=1
then the signal is output until
the bit is set back to 0 . With
SwBuzzer=0
the output signal duration is controlled by the 4bit timer. If neither the
SwBuzzer
or the timer are active, the Buzzer terminal is on 0.
The high impedance state setting with
BzOutEn
is independent of the
SwBuzzer
and Timer settings. As soon
as the bit is set to 1 the Buzzer terminal is set tristate. See also Figure 19.
Figure 19. Melody Generator Block Diagram
BzO utEn
Ck[16]
(from Prescaler)
1
Frequency
G enerator
V
SS
8
Frequency S elect
SwBuzzer
MU
0
BZ
Term inal
FlBuzzer
Control
Logic
A uto
C lose
Zero
IR Q Bz
4 - B it Tim er
Tim er Clock
(from Prescaler)
Control & Status
R egisters
Period R egister
Internal D ata Bus DB[3:0]
7.1 4-Bit Timer
The timer has 2 modes:
- Single run mode (Auto=0)
- Continuos run mode (Auto=1)
Mode selection and timer count down frequency is done in register
RegMelTim.
All timer frequencies are
coming from the prescaler. The 4-bit timer can be used independent of the melody buzzer application.
Whenever the timer reaches 0 it generates an interrupt request
IRQBz
in the register
RegIRQ2
. This interrupt
can be masked with the bit
MaskIRQBz
in register
RegIRQMask2.
By writing 0 into the timer period register the
timer stops immediately and does not generate an interrupt.
03/02 REV. D/444
Copyright
2002, EM Microelectronic-Marin SA
27
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EMMICRO [ EM MICROELECTRONIC - MARIN SA ]
