Panasonic KX-TCD705RUM / KX-TCD705RUS Service Manual ▷ View online
5 CIRCUIT OPERATION (BASE UNIT)
BLOCK DIAGRAM BASEBAND SECTION AND LINE INTERFACE (BASE UNIT)
5.1. THE BASE-BAND SECTION
5.1.1. INTRODUCTION (SEE Fig. 17)
The base-band section consists of a base-band integrated circuit (BBIC), a Flash PROM and an EEPROM.
5.1.2. THE BASE-BAND INTEGRATED CIRCUIT (BBIC)
The PMB6725 (IC8) is a CMOS device designed to handle all the audio, signal and data processing needed in a DECT base
unit. It contains a "burst mode controller" which takes care of DECT specific physical layer and radio section control. It also
contains an ADPCM codec filter used for speech encoding and decoding in the DSP section, a general purpose microcontroller,
various other ADC´s, DAC´s, timers and power control circuitry.
unit. It contains a "burst mode controller" which takes care of DECT specific physical layer and radio section control. It also
contains an ADPCM codec filter used for speech encoding and decoding in the DSP section, a general purpose microcontroller,
various other ADC´s, DAC´s, timers and power control circuitry.
The BBIC interfaces to its external PROM (IC5) via a data/address/control bus. It connects to the EEPROM via a serial
interface, and a second serial interface is used during manufacture and service to connect to an external computer.
interface, and a second serial interface is used during manufacture and service to connect to an external computer.
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5.1.3. FLASH PROM (SEE Fig. 18)
The 2 Mbit (IC5) Flash PROM contains the operational firmware for the microcontroller. It is interfaced to the
data/address/control bus using address lines A0 to A17, data lines D0 to D7, and chip select (pin 30), output enable (pin 32),
and write (pin 7).
data/address/control bus using address lines A0 to A17, data lines D0 to D7, and chip select (pin 30), output enable (pin 32),
and write (pin 7).
5.1.4. EEPROM (SEE Fig. 18)
The electrically erasable PROM PQVIT2432WM6 (IC9) is used to store all the temporary operating parameters for the base
(see EEPROM LAYOUT (BASE UNIT)). It uses a two-line serial data interface with the BBIC, with bi-directional data on pin 5
(TP104), and clock on pin 6 (TP103).
(see EEPROM LAYOUT (BASE UNIT)). It uses a two-line serial data interface with the BBIC, with bi-directional data on pin 5
(TP104), and clock on pin 6 (TP103).
5.1.5. CLOCK GENERATION (SEE Fig. 18)
A single clock generator in the BBIC uses an external crystal X1 to derive all clock frequencies used in the base. The crystal
is tuned to the exact frequency of 10.368 MHz during manufacture.
is tuned to the exact frequency of 10.368 MHz during manufacture.
The BBIC provides a reference clock signal SYRI (pin 21, TP101) which is used to drive the PLL circuitry in the RF module. The
basic data rate for TXDA (pin 14) and RXDA (pin 10) is 1.152 Mbits/s, which is 10.368MHz divided by 9.
basic data rate for TXDA (pin 14) and RXDA (pin 10) is 1.152 Mbits/s, which is 10.368MHz divided by 9.
5.1.6. LOCATOR KEY (SEE Fig. 18)
The “Locator (Page)” button is connected to pin 51 (TP109) of the IC8. When pressed the base transmits a message to the
handset, which then beeps.
handset, which then beeps.
5.1.7. FACTORY SERIAL PORT (SEE Fig. 18)
In order to communicate with the base band section during manufacture and servicing (using a PC) a serial data link has been
provided.
provided.
Serial data input/output is provided through the SDA terminal (J102). The data is clocked through using the SCL terminal
(J103). A ground terminal is provided by J104.
(J103). A ground terminal is provided by J104.
To invoke the external communication mode the MODE_SEL terminal (J101) must be connected to the 2.65V terminal (J100).
The serial port terminals J100 to J104 are connected to by means of test probe pads on the ground plane side of the pcb.
5.1.8. BUZZER CIRCUIT (SEE Fig. 18)
A square-wave signal from IC8 pin 68 is used to sound the buzzer via switching transistor T6 (TP98). Various tones and
cadences are used dependent on function. Buzzer volume is varied by changing the duty cycle of the drive waveform. D16
provides quenching of back-emf generated when T6 turns off.
cadences are used dependent on function. Buzzer volume is varied by changing the duty cycle of the drive waveform. D16
provides quenching of back-emf generated when T6 turns off.
5.1.9. AUDIO PATH-RX AUDIO-LINE INPUT (SEE Fig. 18)
Audio from the line interface TXAF (TP97) enters the BBIC on pin 40. The audio signal passes through the analogue part of the
BBIC where it is amplified and converted to a digital audio stream signal. The burst mode controller processes this stream
performing encryption and scrambling, adding the various other fields to produce the GAP standard DECT frame, assigning to
a time slot and channel etc. to emerge on pin 14 as TXDA.
BBIC where it is amplified and converted to a digital audio stream signal. The burst mode controller processes this stream
performing encryption and scrambling, adding the various other fields to produce the GAP standard DECT frame, assigning to
a time slot and channel etc. to emerge on pin 14 as TXDA.
5.1.10. AUDIO PATH - TX AUDIO - LINE OUTPUT (SEE Fig. 18)
Audio from the receiver RXDA enters the BBIC on pin 10 as GAP standard DECT frames. It passes through the decoding
section burst mode controller where it separates out the frame information and performs de-encryption and de-scrambling as
required. It then goes to the DSP where it is turned back into analogue audio. This is amplified by the analogue front end and
emerges at pin 38 - i.e. the RXAF signal of the line interface.
section burst mode controller where it separates out the frame information and performs de-encryption and de-scrambling as
required. It then goes to the DSP where it is turned back into analogue audio. This is amplified by the analogue front end and
emerges at pin 38 - i.e. the RXAF signal of the line interface.
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KX-TCD705RUM / KX-TCD705RUS
Circuit Diagram
KX
-T
CD7
05RU
M
/
/
K
X
-T
CD7
05RU
S
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5.2. THE LINE INTERFACE SECTION (SEE BLOCK DIAGRAM Fig. 17)
5.2.1. INTRODUCTION
This section consists of the telephone line interface, bell detector, charge-pulse detector, hook switch, pulse dialing circuits,
audio circuits, DC mask & line impedance circuits, power supplies, and battery charger circuits.
audio circuits, DC mask & line impedance circuits, power supplies, and battery charger circuits.
5.2.2. TELEPHONE LINE INTERFACE (SEE Fig. 19)
The telephone line is connected to a bridge rectifier D8. Surge suppressor SA3 protects against excessive line voltages. Test
points are TP40 (A), TP26 (B). A 16 kHz notch filter L3 and L5 block the 16 kHz “charge pulse” signal from the rest of the line
input circuitry. Bridge rectifier D8 provides for lines of either polarity. The output of D8 is “Line +” (TP39) and “Line -” which is
ground.
points are TP40 (A), TP26 (B). A 16 kHz notch filter L3 and L5 block the 16 kHz “charge pulse” signal from the rest of the line
input circuitry. Bridge rectifier D8 provides for lines of either polarity. The output of D8 is “Line +” (TP39) and “Line -” which is
ground.
5.2.3. BELL DETECTOR (SEE Fig. 19)
The AC ringing signal is detected by phoptocoupler IC2, using its internal diode in conjunction with D4. DC from the line is
blocked by C2. The other components D2, D3, and R3 reduce current and increase the circuit impedance in line with national
requirements. When ringing is detected IC2 will turn on, and the RING line will be dragged to a low voltage.
blocked by C2. The other components D2, D3, and R3 reduce current and increase the circuit impedance in line with national
requirements. When ringing is detected IC2 will turn on, and the RING line will be dragged to a low voltage.
5.2.4. CLIP CIRCUITS (SEE Fig. 19)
The CLIP signal is detected by IC3 and sent to the BBIC through the /TXAF line as a square waveform. The CLIP_STATE
signal from the BBIC is used to provide a CLIP impedance through a combination of components selected from R85, R86, C93,
C37, C97 and R1. The combination depends upon the CLIP requirements of the specific country - often there is no
requirements for the CLIP_STATE impedance.
signal from the BBIC is used to provide a CLIP impedance through a combination of components selected from R85, R86, C93,
C37, C97 and R1. The combination depends upon the CLIP requirements of the specific country - often there is no
requirements for the CLIP_STATE impedance.
T10 disables the CLIP signal during the off-hook condition.
Circuit Diagram
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KX-TCD705RUM / KX-TCD705RUS
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