NSAM265SRA datasheet(4/58 Pages) NSC

4 / 58 page

10 Theory of Operation

11 OVERVIEW

The CompactSPEECH is a digital speech processor which

provides Digital Answering Machine (DAM) functionality to

embedded systems such as fax machines or stand-alone

answering machines

The CompactSPEECH processor is based on a powerful

16-bit RISC CPU with Digital Signal Processing (DSP) mod-

ule

However

since the CompactSPEECH firmware is

masked in the internal ROM it requires neither 16-bit nor

DSP programming

The CompactSPEECH processor is designed to operate as

a slave peripheral that is controlled by an external micro-

controller via a simple MICROWIRE based serial link The

microcontroller is responsible for system-level control (eg

buttons display ring detection) while the CompactSPEECH

is responsible for speech and tone operations such as re-

cording playback tone detection and speech synthesis

The NSAM265SR CompactSPEECH supports DRAM and

Audio grade DRAM (ARAM) as a storage device ARAMs

are cheaper than DRAMs which reduces the total system

cost

The NSAM265SR CompactSPEECH has an on-chip DRAM

controller which reduces the chip count for complete DAM

functionality to three (the CompactSPEECH ARAM and a

codec) The CompactSPEECH supports various ARAM con-

figurations and automatically recognizes the actual configu-

ration

The NSAM265SF CompactSPEECH supports FLASH and

Audio grade FLASH (AFLASH) as a storage device A DAM

design which incorporates FLASH technology does not re-

quire a battery backup for the message storage device thus

reducing the system cost and complexity

When necessary the CompactSPEECH can be switched to

power-down mode which considerably reduces the power

consumption of the whole system

The CompactSPEECH includes an on-chip English vocabu-

lary for time-and-day stamp announcements and voice

prompts In addition to the on-chip vocabulary the Com-

pactSPEECH supports external vocabularies (resident on

external ROM or AFLASH) which can be used to implement

voice prompts in various languages Several vocabularies

can be supported simultaneously

This chapter describes the features of the Compact-

SPEECH processor and how they work together

12 THE STATE MACHINE

The CompactSPEECH functions as a state machine It

changes state either in response to a command sent by the

microcontroller after execution of the command is complet-

ed or as a result of an internal event (eg memory full or

power failure)

The CompactSPEECH may be in one of the following

states

RESET

The CompactSPEECH is initialized to this state after a full

hardware reset by the RESET signal (see Section 22)

CompactSPEECH detectors (VOX call progress tones and

DTMF tones) are not active In all other states the detec-

tors are active (See the SDET and RDET commands for

further details)

IDLE

This is the state from which most commands are executed

As soon as a command and all its parameters are received

the CompactSPEECH starts executing the command

PLAY

In this state a message is decompressed and played

RECORD

In this state a message is compressed and recorded into

the message memory

SYNTHESIS

An individual word or a sentence is synthesized from the on-

chip or an external vocabulary

TONE

GENERATE

The CompactSPEECH generates single or DTMF tones

MEMORY

READ

The CompactSPEECH reads a 32-byte block from the mes-

sage memory and sends it to the external microcontroller

MEMORY

WRITE

The CompactSPEECH accepts a 32-byte block from the ex-

ternal microcontroller and writes it to the message memory

MEMORY

FREE

The CompactSPEECH takes memory space that was freed

by the DM and DMS commands and makes it available for

new messages This process occurs only with NSAM265SF

where FLASH memory is used for message storage

After receiving an asynchronous command (see Section

13) such as P (Playback) R (Record) SW (Say Words) or

GT (Generate Tone) the CompactSPEECH switches to the

appropriate state and executes the command until it is com-

pleted or an S (Stop) or PA (Pause) command is received

from the microcontroller

When an asynchronous command execution is completed

the CompactSPEECH switches to the IDLE state

Table 1-1 shows the CompactSPEECH commands the

source states in which these commands are valid and the

result states which the CompactSPEECH enters as a result

of the command

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