EM78P568

8-bit OTP Micro-controller

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* This specification are subject to be changed without notice.

42

01/31/2004

V4.7

VII.9 Signal and control paths for DAC, DAC tone gen., CTCSS and Comparator

DAC Tone

Gen.

R-2R

fm =

447.829kHz

MUX

DA7~DA0

DAT/DAD

DAT7~DAT0

DAST/P67

PORT67

DAO/P67

DATEN

MUX

2.5V

ref

VDD

MUX

VDD

VRSEL

(part of Comparator)

MUX

ASW3

To ladder resistors

To Sub-Audio LPF

(part of CTCSS)

VTX3

VRX3

DAC

DAC Tone Gen.

B2

B1

CMPEN

Name

Register bit location

DAT7 ~ DAT0 RE PAGE1 bit 7 ~ 0

DA7 ~ DA0

RA PAGE1 bit 7 ~ 0

ASW3

DATEN

VREF

DAST/P67

CMPEN

VRSEL

REFSEL

REFEN

REFSEL

REFEN

Volgage reference control logic

Name

Register bit location

DAST/P67

IOCA PAGE1 bit 3

VRSEL

IOCA PAGE1 bit 4

DATEN

IOCA PAGE1 bit 5

VREF

IOCA PAGE1 bit 6

DAT/DAD

IOCA PAGE1 bit 7

CMPEN

IOC5 PAGE1 bit 7

ASW3

IOCE PAGE1 bit 2

ps. REFEN, REFSEL are not register bits.

Fig.16 Signal and control paths for analog circuit

The Fig.16 above try to explain how to use built-in 8-bit R-2R DAC. This DAC can be used as general DAC; here

is call “DAC general mode”. Also it can be used as FRS CTCSS tone generation; here is called DAC tone generator

mode. When you use DAC general mode, you have to software program DAC input data DA7 ~ DA0 bits with

different points of value for tone generation. When you use DAC tone generator mode, you just need to set DAT7 ~

DAT0 bits and then the hardware “DAC Tone Gen.” will auto-program DAC to generate corresponding frequency

signal output. Using this feature, it is easy and software free to generate accurate CTCSS tone.