Panasonic KX-TEA308NE, Service Manual

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11.7. CONTROL CIRCUIT
11.7.1. Composition
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.
11.8. TONE GENERATOR CIRCUIT
11.8.1. Composition
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 sine wave and become 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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KX-TEA308NE