Appendix A. Line Interface - Ricoh FAX220 Service Manual

APPENDIX A. LINE INTERFACE

1. Overall LIU Description
LIU Block Diagram
Filter
Line
Protection
External
Telephone
The LIU (Line Interface Unit) has all the telephone line interface functions and contains a telephone unit which is
powered by the machine when the machine is switched on, and is alternatively powered from the telephone line
when the machine is switched off.
The line interface contains filters, a current sensor, RY1 relay, RY2 relay, and ring detection circuit. The RY1 relay
switches the line connection either to the internal telephone unit or to the modem. The RY2 relay switches the line
either to the external telephone and the ring detection circuit or to the internal dialing circuit.
In standby mode, both relays are switched down to connect the line to the external telephone and the ring detection
circuit. When the internal handset is picked up, the hook switch goes up to connect the line to the dialer and speech
circuit for dialing and voice communication. The RY2 relay is only switched up when the ''On Hook Dial'' key is
pressed for On-hook dialing.
The internal telephone unit contains the handset interface, speech circuit, and a dialer (microcontroller with built-in
CPU, ROM, RAM and DTMF tone generator).
The single tone signals, CNG, CED, dial tone, and busy tone are detected by the modem on the FCE through a
high impedance transformer.
Line Transformer
High Impedance
Transformer
Current
Sensor
RY1 Relay
RY2 Relay
Hook
Switch
DI Relay
Dialer
Ringing
Detection
HSB
A-1
Speaker Volume
Speech
Handset
Circuit
DC/DC
Photocouplers
FCE/
FDU
OPU