KX-TEB308CA, KX-TE82460X, KX-TE82493X, KX-A227X - Panasonic PBX Service Manual (repair manual). Page 9

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     KX-TEB308CA/KX-TE82460X/KX-TE82493X/KX-A227X
4.6.
Explanation of Block Diagram (Main Unit)
4.6.1.
Power Supply Circuit
This power supply unit is a switching power supply. Power supply unit supplies DC voltage (+27V,+15V,3.3V)to main board and
other optional cards. And this unit has an adaptor circuit to back up battery.
4.6.2.
COL Interface Circuit
There are the interface circuits linking the CO line (CO1 -CO3) and the cross point circuit section.
4.6.3.
Cross Point Circuit
This is a space division switching system for connecting the following:
The eight extension circuits with the three CO, DTMF generator, DTMF receiver, INT-CALL ID, MODEM,OGM, BV, paging, music
on hold, tone etc.
It is composed of 3 C-MOS IC's. (8 X 16 matrix: 1pcs and 4 X 8 matrix: 2pce).
4.6.4.
Intercom Circuit
This is the interface circuit of the single line telephone, and it is composed of 8 intercom circuit (ICM1-8).
4.6.5.
Power Failure Through Call Switching Circuit
There is one power failure transfer circuit (CO1-EXT101).
4.6.6.
Data Communication Circuit
The APT i/f module which performs communication with a private telephone machine is built in ASIC.
4.6.7.
Control Circuit
A control block consists of CPU (compatibility with Intel 8086) (IC700), Flash ROM (8Mbit) (IC705) and SRAM (4Mbit) (IC704). 
RTC, Timer, DMAC, USB Controller, WDT, INTC, UART, General Purpose I/O ports, APT i/f and DSP are built into CPU chip.
General purpose I/O block is composed by discrete parts (IC7, IC8) and the I/P port in CPU.
IC7 and IC8 control extension, and the I/O ports in CPU control the COL chiefly.
In order to maintain time, system data and others, RTC (Real Time Clock) in CPU and SRAM are backed up with the lithium battery.
4.6.8.
Tone Generator Circuit
The rectangle wave generated by the timer of CPU is changed into sine wave with a low pass filter, and various tones are gener-
ated.
4.6.9.
DTMF Generator Circuit
DTMF (Dial Tone Multi Frequency) generator is used for dispatch to outside line, and communication with the voice mail connected
to the extension.
4.6.10. DTMF Receiver Circuit
The circuit that receives the Dial Tone Multi Frequency by which extension dispatch is carried out with the DTMF receiver con-
nected to the crossing point.
4.6.11. Int Call ID Circuit
FSK/DTMF generated by DSP in CPU are connected even to a crossing point through AMP. The circuit which sends out a CALLID
signal to the telephone connected to an extension by connecting the line of INT-CALL-ID with arbitrary extensions.
4.6.12. Modem Circuit
The MODEM signal generated by DSP in CPU is connected even to a crossing point through AMP. 
The circuit, which connects the line of MODEM with arbitrary outside line, and enables MODEM communication with outside line.
4.6.13. USB Circuit
The circuit which makes communication possible by PC and 1.1 standards by the USB controller in CPU.
4.6.14. OGM Circuit
The 4M Serial Flash ROM is connected to CPU by the memory controller in DSP (in CPU).
A maximum of 3-minute storing of OGM is possible to a serial flash ROM.
4.6.15. Ring Signal Generator Circuit
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.
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