EM78P568

8-bit OTP Micro-controller

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* This specification are subject to be changed without notice.

44

01/31/2004

V4.7

VII.10 CTCSS block

VII.10.1 Block control and signal flow description

Audio

BPF

VRF

VRF

Rx AMP

MIC AMP

Z C

AURX/P65

RXO

RXI

MICI

MICO

Summing

MTX/P66

VRF

-10dB

0dB

ASW1

ASW2

RXPWR

LPFPWR

BPFPWR

Sub-Audio

LPF

ASW4

MUX

PORT66

MTX

MUX

PORT65

AURX

P65S

P66S

AMP

MUX

ASW3

MUX

MUX

MUX

DETO

TXPWR

TXPWR

RXPWR

VRX1

VTX1

VRX2

VTX2

VRX3

VTX3

VRX4

VTX4

(from DAC output buffer B2)

CTCSS tone input

MUX

MICO

AMUTE

Name

Register bit location

ASW1

IOCE PAGE1 bit 0

ASW2

IOCE PAGE1 bit 1

ASW3

IOCE PAGE1 bit 2

ASW4

IOCE PAGE1 bit 3

LPFPWR

IOCE PAGE1 bit 4

BPFPWR

IOCE PAGE1 bit 5

RXPWR

IOCE PAGE1 bit 6

TXPWR

IOCE PAGE1 bit 7

Name

Register bit location

P65S

IOC6 PAGE1 bit 5

P66S

IOC6 PAGE1 bit 6

AMUTE

IOC6 PAGE1 bit 7

DETO

R7 PAGE1 bit 6

CTCSS block on page 36 Fig.14 is the key feature for FRS baseband signal processing. For receiving path, it

receives the RF demodulator output signal and extract the audio output signal to AURX pin. Also it decodes

CTCSS tone and its decoding data is shown in the DETO. For transmitting path, it combines audio signal from

Mic Amp and CTCSS signal from DAC tone generator(as description in VII.9 section) thru MTX output to RF

modulator input end. CTCSS block consists of amplifiers, analog switch, filters and zero-crossing detector

which descriptions are shown below.

RX AMP : (Receiving amplifier) It accepts RF demodulator output signals which combine demodulated

audio and CTCSS tone. Its bias voltage is VDD/2.

MIC AMP : (Microphone amplifier) It is the audio input amplifier. Its bias voltage is VDD/2.

MUX : (Analog multiplexer switch) It is used for analog signal path switching.

Audio BPF : (Audio band pass filter) This audio BPF has pass band 300Hz ~ 3.4kHz. It is used to let audio

signal pass through and filter out CTCSS tones. It plays an important role in extracting audio signal. Also it

cut out unwanted signal while audio signal transmitting.

Sub-Audio LPF : (Sub-audio low pass filter) This sub-audio LPF has pass band 253Hz. It is used to let

CTCSS tone pass through and filters out audio signal. It plays an important in extracting CTCSS tone. Also

it cut out unwanted signal while CTCSS tone transmitting.

Summing AMP : (Summing amplifier) It is an analog signal mixer for audio signal and CTCSS tone

transmitting. CTCSS tone will be attenuated about 10dB before signal mixing.

ZC : (Zero-crossing detector) This detector transforms CTCSS tone signal from analog form to digital form.

It will be the CTCSS tone detection.