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Chapter 42 Sound Generator
3.Registers
[bit 2] INTE : Interrupt enable bit
This bit enables the interrupt signal of the Sound Generator. When this bit is "1" and the INT
bit is set to "1", the Sound Generator signals an interrupt.
[bit 1] INT : Interrupt bit
This bit is set to "1" when the Tone Pulse counter counts the number of the tone pulses
specified by the Tone Count register and Decrement Grade register.
This bit is reset to "0" by writing "0". Writing "1" has no effect and Read-Modify-Write
instructions always result in reading "1".
[bit 0] ST : Start bit
This bit is for starting the operation of the Sound Generator. While this bit is "1", the Sound
Generator perform its operation.
When this bit is reset to "0", the Sound Generator stops its operation at the end of the current
tone cycle. The BUSY bit indicates whether the Sound Generator is fully stopped.
■ Frequency Data Register (SGFR)
The Frequency Data register stores the reload value for the Frequency counter. The stored value
represents the frequency of the sound (or the tone signal from the toggle flip-flop). The register
value is reloaded into the counter at every transition of the toggle signal.
The following figure shows the relationship between the tone signal and the register value.
It should be noted that modifications of the register value while operation may alter the duty cycle
of 50% depending on the timing of the modification.
■ Amplitude Data Register (SAGR)
The Amplitude Data register stores the reload value for the PWM pulse generator. The register
SGFR
Bit number
15 14 13 3 2 1 0
D15 D14 D13 D3 D2 D1 D0
(R/W) (R/W) (R/W) (R/W) (R/W) (R/W) (R/W)
(X) (X) (X) (X) (X) (X) (X)
Read/write
Initial value
Frequency Data register
Address: 00019AH
One Tone Cycle
(register value+1) x
One PWM cycle
(register value+1) x
One PWM cycle
Tone signal
15 14 13 12 11 10 9 8
D7 D6 D5 D4 D3 D2 D1 D0
SGAR
(R/W) (R/W) (R/W) (R/W) (R/W) (R/W) (R/W) (R/W)
(0) (0) (0) (0) (0) (0) (0) (0)
Bit number
Read/write
Initial value
Amplitude Data register
Address: 00019CH