Specifications

Telephone Interface 61
4.2 North American Telephone Line Interface
This section briefly describes the DECvoice TLI designed for use in North
America.
4.2.1 TLI to Telephone Line Connection
The circuit that connects the TLI to the telephone network must meet
certain North American telephone regulations, provide access to the
network, and protect the TLI circuitry. The TLI connects to the telephone
line through modular telephone jacks for RJ11 service.
The circuitry that connects the TLI to the telephone network provides the
following features.
• Ring detection
• Line current interruption (wink) detection
• Hook control
• A protected analogue path
• Protection against surges in telephone line current
4.2.2 TLI to DTC04 Module Connection
The TLI connects to the module through a modification of the Intel
Subscriber Line Datalink protocol. This protocol is described in more
detail in Section 4.1. Make sure you read this section before you continue.
Briefly, the Intel SLD protocol is a master-slave system for connecting
a computer to the telephone network. The master half of the system
controls the rate and direction of data flow over the telephone network.
The master controls the flow of data by sending a clock signal (SCL) and
a directional signal (SDIR) to the slave. In the DECvoice system, the TLI
is the SLD master, the DTC04 module is the slave.
4.2.2.1 Data Flow Control
The TLI contains a circuit that provides the clock signals for all the
telephone lines in a DECvoice system. This circuit generates the 512 kHz
clock signal and SDIR signals for the DTC04 module and the 29C50 chips.