AN2274 Freescale Semiconductor / Motorola, AN2274 Datasheet - Page 5

• Manufacturer Part Number: AN2274
• Description: Generic Tone Generation on the StarCore SC140 Core
• Manufacturer: Freescale Semiconductor / Motorola

2.1 Elementary Components
The elementary tone component is a pair composed of a sound period followed by a silence period (see Figure 2).
This pair (sound + silence) can be repeated as often as needed to yield a component. In the example shown in
Figure 1, each component has only one consecutive occurrence of its base pair.
Each component is defined by the following parameters:
Freescale Semiconductor
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Frequencies (in Hz).
Levels (in dBm0). The signal amplitude per frequency is given as follows:
Sound duration. Indicates the duration of the sound (in ms).
Silence duration. Indicates the duration of the silence period (in ms) that follows the sound period. The
software fills in the linear_out buffer with zeroes to cover that period. A value of zero indicates no
silence period.
repeat_component. This value specifies the number of pairs (sound + silence) that must be generated
to complete the component. A value of zero indicates that the pair should be repeated indefinitely.
Control word. Defines whether the two sinusoids are to be added or modulated, the initial phase (0 or
180°), and the frequency unit (f or f/3). This flag is stored in a byte as follows:
Bit 0: Add/Mod
— 0
— 1
7: MSB
Sound
—
PAIR (Sound + Silence)
The two frequencies are added.
The two frequencies are modulated.
Generic Tone Generation on the StarCore™ SC140/SC1400 Cores, Rev. 1
—
6
Silence
Number of pair repetition: repeat_component
Figure 2. Elementary Tone Component
—
5
A
=
Phase_2
10
4
–
Component
Level
. . . .
. . . .
(
dBm0
Phase_1
3
) 20
⁄
Sound Duration
⁄
Sound
2
Unit_2
2
Tone Generator Implementation
Unit_1
1
Silence Duration
Silence
Add/Mod
0:LSB
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