Sunplus Technology Co., Ltd.

Rev.: 1.1

1999.11.19

SPC21A1

5

TIMER/COUNTER

The SPC21A1 contains two 12-bit timer/counters, TMA and TMB respectively.

TMA can be specified as a

timer or a counter, but TMB can only be used as a timer.

In the timer mode, TMA and TMB are re-loaded up-

counters.

When timer overflows from $0FFF to $0000, the carry signal will make the timer automatically reload

to the user’s pre-set value and be up-counted again. At the same time, the carry signal will generate the INT

signal if the corresponding bit is enabled in the INT ENABLE Register.

If TMA is specified as a counter, users

can reset by loading #0 into the counter. After the counter has been activated, the value of the counter can also

be read from the counters at the same time.

The read instruction will not affect the value of the counter or reset

it.

Clock source of Timer/Counter can be selected as follows:

Timer/Counter

Clock Source

12-BIT TIMER

CPU CLOCK (T) or T/4

TMA

12-BIT COUNTER

T/64, T/8192, T/65536 or EXT CLK

TMB

12-BIT TIMER

T or T/4

MODE SELECT REGISTER

TMA only, select timer or counter

TIMER CLOCK SELECTOR

Select T or T/4

SPEECH AND MELODY

Since the SPC21A1 provides a large ROM and wide range of CPU operation speeds, it is most suitable for

speech and melody synthesis.

For speech synthesis, the SPC21A1 can provide NMI for accurate sampling frequency.

Users can record or

synthesize the sound and digitize it into the ROM.

The sound data can be played back in the sequence of the

control functions as designed by the user's program.

Several algorithms are recommended for high fidelity and

compression of sound including PCM, LOG PCM, and ADPCM.

For melody synthesis, the SPC21A1 provides the dual tone mode.

After selecting the dual tone mode, users

only need to fill either TMA or TMB, or both TMA and TMB to generate expected frequency for each channel.

The hardware will toggle the tone wave automatically without entering into an interrupt service routine.

Users

are able to simulate musical instruments or sound effects by simply controlling the envelope of tone output.