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If an AC power failure lasts longer than one second (momentary power failure), the COL is directly connected to the extension.
The COL1 will be connected with EXT101.
When power failure, RL200 switches from EXT-line to CO [T/R].
*In case of KX-TEM824, and the COL4 will be connected with EXT109.
*In case of KX-TE82480, and the CO7 will be connected with EXT117.

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This circuit is composed of the ASIC and the data communication interface circuits for the ICM circuit.

The APT I/f module is built into the CPU. It is for the APT communication of one block (8ch) and has the module of three blocks
(24ch) at maximum. 
Selection signal of 3 bits to select 1ch out of 8chs is common to each block.
The APT I/f module switches the communication point every 4ms in the ports 1-8/9-16/17-24 of the extension as follows:
#101

→#102→#103→#104.....→#108→#101.....,

#109

→#110→#111→#112.....→#116→#109.....,

#117

→#118→#119→#120.....→#124→#117.....,

In the case where the extension is not connected with the APT, it is recognized as an SLT connection and a dummy communica-
tion is performed.

Interface block diagram of ASIC and ICM

23

When ASIC send the request signal to the proprietary telephone and after receiving the key input information (19 pulses) from
the proprietary telephone and sending data (47 pulses) for LED control. 4bit CPU will receive acknowledge signal from the pro-
prietary telephone.
a) Reception 
The data from the proprietary telephone is received via H and L lines along the path shown below.
H.L line 

→ C208 → IC200 →T201 → R235 → Q210 → ASIC

b) Transmission
The data to the proprietary telephone is transmitted along the following Path. 
ASIC 

→ Q209 → Q215 → T201 → IC200 → C208 → H.L line

The control block is composed of the 16bit CPU(IC700: operating on 23.966MHz system clock from the 47.936MHz external crystal
oscillator), the 8Mbit Flash ROM, the 4Mbit SRAM, and the ASIC for the I/O Port to control the outside line.
The port to control the extension, the clock IC, the address decoder, and other CPU Peripheral circuit are included in the
IC700.Also, the IC700 includes functions such as Extension CID(FSK, DTMF), MODEM sending/receiving, BGM, OGM recording/
playing, DTMF tone, CNG tone, CPT tone, and VOX detection.
The SRAM has a lithium battery to back up information such as speed dial, date, dial data, and system data etc. The battery also
backs up the clock IC in the IC700.
I/O Port to control extension circuit, clock IC, address decoder, and other CPU Peripheral function are included in IC700. And IC700
include the functions as transmission of Extension Caller ID, transmission & receive of MODEM, transmission BGM, recording &
playing of OGM, detect of DTMF tone, CNG tone, CPT tone & VOX.
the SRAM has a lithium battery as back up for protection of the memory of information of such as the speed dial, date, dial data, and
system data, etc. This battery is back up clock IC in IC700 too.

24

This system has three different tones, 620Hz, 440Hz, 350Hz.
ASIC make the 350Hz, 620Hz and 440Hz square wave signals. 
The 350Hz and 440Hz square wave signals are shaped by the low pass filter to sin wave and become tone 1.
On the other hand, 620Hz, square wave signal is shaped by the low pass filter to sin wave and becomes tone 2.
Tone signals 1 and 2 turn ON and OFF at the cross point, thus dial tone, busy tone, and other tones, are produced.