Pulse-Width Tone
7-54
Table 7–45. PWT Frequency Control Register (FRC) – Offset address (hex): 0x00
Bit
Name
Function
R/W
Reset
Value
5–2
FRQ
Frequency selection (12 frequencies)
Resynchronized writing, asynchronous reading
R/W
0000
1–0
OCT
Octave selection
Resynchronized writing, asynchronous reading
R/W
00
Table 7–46. PWT Volume Control Register (VRC) – Offset address (hex): 0x04
Bit
Name
Function
R/W
Reset
Value
6–1
VOL
Volume selection
Resynchronized writing, asynchronous reading
R/W
000000
0
ONOFF
Switch ON/OFF tone (on: 1, off: 0).
Resynchronized writing, asynchronous reading
R/W
0
Table 7–47. PWT General Control Register (GCR) – Offset address (hex): 0x08
Bit
Name
Function
R/W
Reset
Value
1
TESTIN
Divider 1/154 switched ON/OFF (on: 0, off: 1).
Asynchronous writing and reading
R/W
0
0
CLK_EN
PWT clock enable (clock disabled: 0, clock enabled: 1).
Asynchronous writing and reading
R/W
0
7.7.4
PWT Programming
7.7.4.1
Buzzer Frequency
To obtain the required frequencies, the PWT clock is divided in a special way.
Four frequency dividers with the coefficients
101
/
107
,
49
/
55
,
50
/
63
,
and
80
/
127
are
connected in series and can be enabled with the four frequency selection bits
(FRQ) in the frequency register. If a divider is not enabled, the clock passes
through the divider without any change so different frequencies can be
produced. After this a multiplexer can choose between this clock, divided by
2/4/8 or 16. The frequency is always halved (this unit is called an octave). Due
to this, the PWT has a range of four octaves.