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Chapter 42 Sound Generator
3.Registers
value represents the amplitude of the sound. The register value is reloaded into the PWM pulse
generator at the end of every tone cycle.
When the DEC bit is "1" and the Decrement counter reaches its reload value, this register value is
decremented by 1(one). And when the register value reaches "00", further decrements are not
performed. However the sound generator continues its operation until the ST bit is cleared.
The following figure shows the relationship between the register value and the PWM pulse.
When the register value is set to "FF", the PWM signal is always "1".
■ Decrement Grade Register (SGDR)
The Decrement Grade register stores the reload value for the Decrement counter. They are
prepared to automatically decrement the stored value in the Amplitude Data register.
When the DEC bit is "1" and the Decrement counter counts the number of tone pulses up to the
reload value, the stored value in the Amplitude Data register is decremented by 1 (one) at the
end of the tone cycle.
This operation realizes automatic decrement of the sound with fewer number of CPU
interventions.
It should be noted that the number of the tone pulses specified by this register equals to "register
value +1". When the Decrement Grade register is set to "00", the decrement operation is
performed every tone cycle.
■ Tone Count Register (SGTR)
The Tone Count register stores the reload value for the Tone Pulse counter. The Tone Pulse
counter accumulate the number of tone pulses (or number of decrement operations) and when it
One PWM Cycle
00h
Register value
One input clock cycles
80h
256 input clock cycles
129 input clock cycles
255 input clock cycles
FEh
FFh
256 input clock cycles
7 6 5 4 3 2 1 0
SGDR
Bit number
Read/write
Initial value
Decrement Grade register
Address: 00019FH
(R/W) (R/W) (R/W) (R/W) (R/W) (R/W) (R/W) (R/W)
(X) (X) (X) (X) (X) (X) (X) (X)
D7 D6 D5 D4 D3 D2 D1 D0
15 14 13 12 11 10 9 8
SGTR
(R/W) (R/W) (R/W) (R/W) (R/W) (R/W)
(X) (X) (X) (X) (X) (X)
Bit number
Read/write
Initial value
Tone Count register
Address: 00019EH
D7 D6 D5 D4 D3 D2 D1 D0
(R/W) (R/W)
(X) (X)