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EM78910AAH

8-BIT MICRO-CONTROLLER

ELAN Microelectronics 

EM78910/910A

8-bit Micro-controller

VII.12 Stuttered dial tone (SDT) Function Description

TIP

RING

FSK block

DATA

/CD

Stuttered Dial

Tone

detection block

/SDT

Fig.17 Stuttered dial tone block diagram

SDT (Stuttered dial tone) circuit and FSK circuit use the same input OP Amp. When SDTPW bit (IOCA

bit5) is set, SDT circuit is powered on and SDT detection is enabled. SDT detection enabled means it is

powered on and detects 350Hz plus 440Hz dual tone frequency. And SDT signal detection output is sent to /SDT

bit (R3 bit5) with low enable. If SDT circuit works, it consists of high-band and low-band band pass tone filters, level

detect, frequency counting and digital algorithm to qualify correct timing.

VII.13 MEI and RTF Function Description

VDD

20M

VDD

MEI

1.2V

1.2M

MEIO

105

220k

RTF

RTF RTFO

330k

3.3M 333

Fig.18 MEI & RTF

Based on TIA/EIA-777 (or TIA SP-4078) protocol, MEI (Multiple Extension Internetworking) allows

Type 2 (and 3) CPE to dynamically arbitrate responsibility for completing the CAS-ACK handshake. Also, RTF

(Request to Flash) allows Type 2 (and 3) CPE to synchronize line flash signal after CAS-ACK handshaking.

For MEI part, protocol shows line voltage below 19V as line-in use (phone off-hook status) and voltage

above 21V as line high (phone on-hook status). MEI circuits works as on-hook/off-hook detection and internal

transition voltage is 1.2V. Use two external resistors to reduce line DC voltage into MEI input pin. These has a

little voltage transition hysteresis to complete the rule.

For RTF part, protocol shows 0.5V line DC voltage change detection and timing to be followed (see the

protocol for details). RTF circuit can detect this little DC voltage change and complete the same timing as

protocol shown.

__________________________________________________________________________________________________________________________________________________________________

* This specification are subject to be changed without notice.

~ 23~

2001/01/12

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