6.8. NCU SECTION6.8.1. GENERALThis section is the interface between the telephone line and external telephone. It is composed of an EXT. TEL line relay (RL101),bell detection circuit, pulse dial circuit, TAM interface circuit, line amplifier and sidetone circuits and a multiplexer.6.8.2. EXT. TEL. LINE RELAY (RL101)1. Circuit OperationNormally, this relay switches to the external telephone side (break) and switches to the open side (make) while OFF-HOOK.{ IC501 (38) High Level → CN501 (5) High Level } → CN101 (5) High Level → Q103 ON → RL101 (make)6.8.3. BELL DETECTION CIRCUIT1. Circuit OperationThe signal waveform for each point is indicated below. The signal (low level section) input to pin 39 of ASIC IC501 on the digitalboard is read by ASIC and judged as a bell.TEL LINE → PC102 (1, 2 - 4) → IC501 (39)6.8.4. TAM INTERFACE CIRCUITThis circuit is to switch between FAX receiving and the external TAM’s message recording automatically. This circuit consists of anEXT. TAM OFF-HOOK detect circuit, monitor transformer, multiplexer, amplifier, and VOX detect circuit.For details, please refer to 6.10. TAM INTERFACE SECTION(P.167).164KX-FP81BX / KX-FP81CX / KX-FP82CX
