RC8650 datasheet(21/48 Pages) ETC

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RC8650 VOICE SYNTHESIZER

RC SYSTEMS

This section describes the operating characteristics of the DoubleTalk

RC8650 chipset.

OPERATING MODES

The RC8650 has four primary operating modes and two inactive

modes designed to achieve maximum functionality and ﬂexibility. The

operating mode can be changed anytime, even on the ﬂy, by issuing

the appropriate command to the RC8650.

Note The RC8650 will not begin speaking until it receives a CR (ASCII

13) or Null (ASCII 00) character—this ensures that a complete contex-

tual analysis can be performed on the input text. If it is not possible for

the application to send a CR or Null at the end of each text message,

use the Timeout Delay command.

The RC8650 does not make any distinction between uppercase and

lowercase characters—text and commands may be sent in any com-

bination of uppercase and lowercase. All data sent to the RC8650

is buffered in an internal 2 KB input buffer, allowing additional text

and commands to be queued even while the RC8650 is producing

output.

Text-to-speech mode. All text sent to the RC8650 is automatically

translated into speech by the integrated DoubleTalk TTS engine. TTS

mode can be further subdivided into three translation modes: Text,

which reads text normally; Character, which reads (spells) one charac-

ter at a time; and Phoneme, which allows the TTS engine’s phonemes

to be directly accessed. TTS mode is the default operating mode.

RealTime Audio Playback mode. Data sent to the RC8650 is written

directly to the RC8650’s audio buffer. This results in a high data rate,

but provides the capability of producing the highest quality speech, as

well as sound effects. PCM and ADPCM data types are supported.

Prerecorded Audio Playback mode. This mode allows recorded

messages and sound effects that have been stored in the RC8650 to

be played back. PCM and ADPCM data types are supported.

Tone Generator modes. These modes activate the RC8650’s musi-

cal tone generator, sinusoidal generator, or DTMF generator. They can

be used to generate audible prompts, music, signaling tones, dial a

telephone, etc.

Idle mode. To help conserve power in battery-powered systems, the

RC8650 automatically enters a reduced-power state whenever it is

inactive. Data can still be read and written to the RC8650 while in this

mode. Current draw is typically 700 µA @ 3.3 V.

Standby mode. This mode powers down the RC8650, where current

draw is typically only 2 µA. Standby mode can be invoked from either

the STBY# pin or with the Sleep command. Data cannot be read from

or written to the RC8650 in this mode.

SECTION2:PRINCIPLESOFOPERATION

TRANSLATION ACCURACY

Because the RC8650 must handle the highly irregular spelling system

of English, as well as proper names, acronyms, technical terms, and

borrowed foreign words, there inevitably will be words that it will mis-

pronounce. If a word is mispronounced, there are three techniques

for correcting it:

1. Spell the word phonetically for the desired pronunciation.

2. Redeﬁne the way the word should be pronounced by creating an

exception for it in the RC8650’s exception dictionary. This method

allows words to be corrected without having to modify the original

text, and it automatically corrects all instances of the word. Excep-

tion dictionaries are covered in detail in Section 4.

3. Use the RC8650’s Phoneme mode.

The ﬁrst technique is the easiest way to ﬁne tune word pronuncia-

tions—by tricking the RC8650 into the desired pronunciation. Among

the more commonly mispronounced words are compound words

(baseball), proper names (Sean), and foreign loan words (chauffeur).

Compound words can usually be corrected by separating the two

words with a space, so that “baseball” becomes “base ball.” Proper

names and foreign words may require a bit more creativity, so that

“Sean” becomes “Shon,” and “chauffeur” becomes “show fur.” Het-

eronyms (words with identical spelling but different meanings and pro-

nunciations) can also be modiﬁed using this technique. For example, if

the word read is to be pronounced “reed” instead of “red,” it can simply

be respelled as “reed.”

COMMANDS

The commands described in the following pages provide a simple yet

ﬂexible means of controlling the RC8650 under software control. They

can be used to vary voice attributes, such as the volume or pitch, to

suit the requirements of a particular application or listener’s prefer-

ences. Commands are also used to change operating modes.

Commands can be freely intermixed with the text that is to be spoken,

allowing the voice to be dynamically controlled. Commands affect only

the data that follows them in the data stream.

Command Syntax

All RC8650 commands are composed of the command character,

a parameter n comprised of a one to four-digit number string, and a

single string literal that uniquely identiﬁes the command. Some com-

mands simply enable or disable a feature of the RC8650 and do not

require a parameter. The general command format is:

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