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CHAPTER 25 SOUND GENERATOR
25.2.5
Tone Count Register
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 reaches the reload value it sets the INT bit. They are intended to
reduce the frequency of interrupts. The register value is reloaded into the counter at
Tone Pulse counter underflow, Decrement counter underflow, and falling edge of tone
signal.
■ Tone Count Register
The count input of the Tone Pulse counter is connected to the carry-out signal from the Decrement counter.
And when the Tone count register is set to "00
from the Decrement counter. Thus the number of accumulated tone pulses is;
((Decrement Grade register) +1) × ((Tone Count register) +1)
i.e. When the both registers are set to "00
542
bit
15
14
13
12
Address:
003549
H
D7 D6 D5 D4 D3 D2
R/W R/W R/W R/W
11
10
9
8
SGTR
D1 D0
Initial value
X X X X X X X X
R/W
R/W
R/W R/W
", the Tone Pulse counter sets the INT bit every carry-out
H
", the INT bit is set every tone cycle.
H
B
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