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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 discrete logic IC (IC7, IC8) for the I/O Port to control the extension.
The port to control the CO, 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 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.

This system has two different tones, 620Hz, 425Hz.
ASIC make the 620Hz and 425Hz square wave signals. 
The 425Hz square wave signal is shaped by the low pass filter to sine wave and becomes tone 1.
On the other hand, 620Hz, square wave signal is shaped by the low pass filter to sine 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.

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A DTMF tone is generated by the DSP in the CPU and sent to an CO line.

The DTMF receiver circuit is composes of four DTMF receivers.
IC606 and IC607 are used for the DTMF receivers from SLT connected to the extension.
The DTMF signal is the 4bit parallel data and read by CPU.

By using the DSP built into the ASIC, it is possible to produce CALLID signal and send it through the cross point to each extension. 
The CALLID signal can be switched between FSK and DTMF. There are two sources of the extension CALL ID in the system.

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The ASIC incorporates a modem function. There is no specified line and modem communication from any line is possible. The
modem communication speed is 2400bps and the system programming rewrite can be operated at the equivalent of 9600bps at
maximum by using software compression technology.

This unit have one USB port for using PC programming. ASIC have USB 1.1 controller inside, so this unit make up USB interface
only ASIC and USB connector.

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The TEB308 model incorporates the functions of OGM, CNG and DTMF detection. At the OGM recording, it changes the analog
sound in the DSP of the ASIC into a digital signal of 16bits by A/D conversion. Then, the data is compressed (encoded) and stored
in a 4M serial flash. Conversely, when being recovered the data stored in the 4M serial flash are decompressed to 16-bit digital
data, and then reproduced as an analog sound after the D/A conversion. The recording/reproducing is achieved by connecting the
path from external line through the cross point to the ASIC.The waveform coding method used at the recording/reproducing stage is
the LD-ADPCM method. The DSP compresses the sound and stores the 4M serial flash using the memory management software in
the DSP. The unit has the recording/reproducing function of 1CH as an initial mounting.The recording time of the OGM is three min-
utes at maximum.
Also, the CNG and DTMF detection are the functions operated in conjunction with the OGM and realized by the DSP in the ASIC.

This section generates the ring signal for the single line telephone. A 20/25Hz square wave is generated by the CPU timer and sent
to low pass filter and the Ring signal is amplified by BELL amplifier circuit, and then passed it through the ringing signal switching
relay to the single line telephone.