NSAM265SR Datasheet, PDF (4/58 Pages) National Semiconductor (TI) – CompactSPEECH Digital Speech Processors

1 0 Theory of Operation
1 1 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 (e g
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
1 2 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 (e g 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 2 2)
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
1 3) 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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