AS3502 datasheet(7/29 Pages) AMSCO

7 / 29 page

REV. M

Page 7

September 1998

AS3502

T/2

R0 < T/2

Start Melody

TRO+

TRO-

R0 < T/2

PW = 1

Burst=1

Pulse Width Volume Control

Sequencer

The sequencer controlling the synthesizer is a six

step rotating shift register that is controlled by a

cadence counter. Each location in the two sequence

control registers (SC1, SC2) contains the value of one

out of three different frequencies or the value of a

tone pause that are played in consecutive order. In

DTMF mode the 6-bit shift register is split up into two

3-byte shift registers. In this mode the cadence steps

are interleaved as S1/S4, S2/S5, S3/S6 where the

SC1 register defines the high group tones with an

attenuation of 2.5 dB and where the SC2 register

defines the low group tones.

MUX

Single Tone:

Dual Tone:

SC1

SC2

Tone Sequencer

Cadence Generation

The cadence counter determines the sequencer

rotation speed and the on/ off timing characteristics of

the tones and controls both the sequencer shift clock

and the tone synthesizer on/ off time. The tone off

time allows to insert pauses on switching from one

frequency to the other.

Cadence Period (CP) and Cadence On Time (CO)

are programmed with an 8-bit value. The CS bit

defines two time spans with different resolution:

CP: Cadence Period

CO: Cadence On Time

Cadence Counter

Repetition Counter

The repetition counter controls either the duration

(RO) and repetition (RP) of the melody sequence or

the volume for pulse width volume control of the tone

ringer output.

In repetition mode the repetition counter may be

operated in continuous mode where the ringing signal

is turned on and off with the RP and R0 period or in

single shot mode where the ringing signal is active for

the R0 period. only.

Each tone signalling sequence must be started with

this counter:

Repetition Period (RP) and Repetition On Time (RO)

are programmed with an 8-bit value .

RP: Repetition Period

RO: Repetition On Time

Repetition Counter

PCM Serial Interface

The AS3502 5-wire PCM port interfaces directly to

many serial port standards. The PCM data word is

either formated in 16-bit linear format with 13 bit 2`s

complement data justified left where the last three

LSB bits are reserved or formatted according to 8-bit

A-Law format with alternate mark inversion (AMI)

meaning that the even bits are inverted per CCITT

G711 specification.

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