HT9480 datasheet(20/57 Pages) HOLTEK

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Timer/event counter

Programmable tone generator

In the case of the programmable timer counter

and a timer/event counter OFF condition, writ-

ing data to their preload registers also reloads

that data to their counters. But if the program-

mable timer counter or the timer/event counter

is turned on, data written to the counter is kept

only in its preload register, and the counter still

goes on operating until an overflow occurs.

After the counter (reading TMR0 or TMR1) is

read, the clock is blocked to avoid errors. The

programmer should take clock blocking into

consideration, since this may result in timing

counting errors.

Programmable tone generator

The programmable tone generator is imple-

mented in the HT9480. The programmable tone

generator contains an 8-stage programmable

frequency divider (mapping to the 1DH address

of the

µC), a 4-stage programmable frequency

prescaler (set by SPF10 and SPF11), and a fre-

quency source selector (set by SPF17). When

1DH=00H, the tone generator is disabled and

BZ outputs high. But when 1DH is of any value

greater than zero the generator is enabled. The

value of the frequency divider, ranging from

2~256, is always greater than the assigned

value by 1. The output of the 8-stage divider is

divided by 2 to generate an output of (1/2 or 1/4)

duty cycle on BZ. The 4-stage programmable

frequency prescaler is shown below.

SPF10 SPF11 Prescaler Divider Factor

The above setting of the prescaler divider factor

is designed for applications on melodies or

sound effects.

The frequency source selector is set by SPF17.

When SPF17=0, the value of the frequency

source selector is the system clock. On the other

hand, when SPF17=1, the value of the selector

turns out to be 32.768kHz. For instance, if the

HT9480

23th Feb ’98

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