84C44X datasheet(14/38 Pages) PHILIPS

14 / 38 page

October 1994

Philips Semiconductors

Product speciﬁcation

8-bit microcontrollers with OSD and VST

84C44X; 84C64X; 84C84X

10 AFC INPUT

The AFC input is used to measure the level of the

Automatic Frequency Control signal. This is achieved by

comparing the AFC input signal with the output of a 3-bit

DAC as shown in Fig.14. DAC analog switches select one

of 8 resistor taps connected between VDD and VSS.

Consequently, eight different voltages may be selected

(see Table 4). The compare signal AFCC, can be tested to

determine whether the AFC input is higher or lower than

the DAC level.

The AFC input shares the same pin as the Derivative Port

line DP1.7. Setting the enable bit AFCE to:

• Logic 1, selects the AFC function

• Logic 0, selects the Derivative Port DP1.7 function.

Table 4

Selection of Vref

AFC2 AFC1 AFC0

Vref

(for VDD = 5.0 V)

VDD × 0.125

0.625 V

VDD × 0.250

1.250 V

VDD × 0.375

1.875 V

VDD × 0.500

2.500 V

VDD × 0.625

3.125 V

VDD × 0.750

3.750 V

VDD × 0.875

4.375 V

VDD

5.000 V

handbook, full pagewidth

COMPARATOR

3-BIT DAC

DP1.7 / AFC

AFC2

AFC1

AFC0

AFCE

AFCC

internal bus

inner latches

DP1.7

MCD178

Fig.14 AFC circuit.

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