MAS9191A datasheet(16/36 Pages) MAS

16 / 36 page

DA9191A.000

July 31, 1997

FUNCTIONS

◆ SAT detection & regeneration

SAT detection is active on voice channel in AMPS or

TACS mode (SYS1=0). The supervisory audio tone is

detected with a digital PLL. The detector compares the

received SAT to the given SAT color code (SCC).

When the given SAT is detected the SATDET bit of

SATDET will cause the interrupt SATINT. On the voice

channel the SAT regeneration can be enabled with bit

SATEN of register 14HEX. By setting bit NOMSAT of

Otherwise, the SAT output frequency will follow

received SAT frequency. The block is in power down

mode when the TXSIP (transmit section in power

down) bit is active in register 07HEX. After a reset the

block is in power down mode.

SCC1

SCC0

SAT frequency

5970 Hz

6000 Hz

6030 Hz

invalid code

◆ SAT, ST or Data Transmission

The SAT and signaling tone (ST) are sent only on

the voice channel in AMPS or TACS mode

(SYS1=0). The SATEN and STON can be used to

control the SAT and ST transmission. However, the

device will automatically stop transmitting SAT and

ST signals whenever data is being transmitted, even

though SATEN or STON is high. The signaling tone

is 8kHz in ETACS and 10kHz in AMPS. Also, switch

S17 for TX data and switch S18 for ST can be used

to disable the transmission. The switches must be on

during transmission. The control bits for these

switches are located in register 0DHEX. The SAT,

TXDATA and the ST are summed and amplified with

GC8. The gain of the amplifier is -3.75dB...+3.75dB

with 16 steps. The adjustment is made with bits 0..3

of register 0DHEX. After being amplified the signal is

filtered with 4th order SC filter F12. The cutoff

frequency of the filter is 19kHz in AMPS, 15kHz in

ETACS and 200Hz in NAMPS (SYS1=1). The gain of

the filter at 1kHz is 0dB. In the NAMPS mode, the

signal is then fed to low pass filter F15, which is a

2nd order RC type filter. After filtering the signal is

summed to the TX audio signal depending on the

state of switch S20. The switch is controlled by bit 6

of register 01HEX .Register 07HEX bit AUDIOP is used

to set these blocks into power down mode.

◆ DTMF Receiver

For enabling answering machine functions, the chip

has an internal DTMF receiver. The receiver is in

power down mode after a reset. The DTMFRP bit of

mode. The receiver has two separate filters for

separation of the low and high frequencies. The

comparator and logic section measures the low and

high frequency periods with an averaging algorithm.

When the valid DTMF tone is detected the external

steering logic output pin EST is set to high. With an

external RC time constant the tone detect time and

tone dropout times can be adjusted. The STGT

input/output pin has an internal comparator and pull-

up and pull-down transistors. When EST is active

and STGT goes from below to above the Vref level

(VDD/2) the STGT is pulled up with an internal

transistor. This causes the STD signal to go high,

which causes the XINT line to become active. At the

same time the detected DTMF tone is stored in

the EST will go low, which causes the STGT to fall.

When the STGT falls below the Vref level (VDD/2)

the internal logic pulls the input down. The external

RC circuit will filter out very short gaps in the

received DTMF tone. The interrupt caused by the

DTMF detector is cleared by reading status register

10HEX. If the interrupt is cleared but register 04HEX is

not read until the next DTMF tone is received, then

the previous tone will be lost. The formula below can

be used to calculate tone present and tone absent

times. By adding diodes to the external circuit the

tone present and tone dropout times can be altered.

If one of the diodes is removed, the absent and

present times are calculated using the parallel

combination of R1 and R2.

EST

STGT

EST

STGT

Time = R*C ln(VDD/VREF)

MAS9191A 数据表(PDF) 16 Page - Micro Analog systems

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