PCA84C846 View Datasheet(PDF) - Philips Electronics

Part Name

Description

Manufacturer

PCA84C846

Microcontrollers for TV tuning control and OSD applications

Philips Electronics 

Philips Semiconductors

Microcontrollers for TV tuning

control and OSD applications

Preliminary specification

PCA84C646; PCA84C846

8 AFC INPUT

The AFC input is intended to measure the level of the

Automatic Frequency Control (AFC) signal. This is done

by comparing the AFC signal with the output of a 4-bit

digital-to-analog converter as shown in Fig.11. The DAC

analog switches select one of the 16 resistor taps that are

connected between VDD and VSS (controlled by bits

AFCV3, AFCV2, AFCV1, AFCV0; Derivative Register 20).

The AFCC signal (bit 0 in Derivative Register 20) then can

be tested to check whether the AFC input is higher or lower

than the DAC level.

The AFC inputs AFC0, AFC1 and AFC2 share the same

pins as Derivative Port lines DP10, DP11 and DP12. The

pin functions are selected by bits AFCE0, AFCE1, AFCE2

(AFC enable/disable bits; Derivative Register 22); for

selection see Table 6.

AFCH1 and AFCH0 (Derivative Register 20) select one

out of three AFC inputs to the comparator; for a correct

comparison, enable the corresponding AFC input (AFCi)

as shown in Table 7.

The conversion time of the AFC is greater than 6 µs but

less than 9 µs. It is recommended to add a NOP instruction

between the instruction which changes Vref or channel

selection and the instruction which reads the AFCC bit

(compare bit).

If the compare bit:

• AFCC = 0, then the AFC voltage < Vref.

• AFCC = 1, then the AFC voltage > Vref.

Table 6 Selection of pin function DP1i/AFCi (i = 0, 1, 2)

BIT VALUE

AFCE2 1

0

AFCE1 1

0

AFCE0 1

0

PIN FUNCTION

DP12

AFC2

DP11

AFC1

DP10

AFC0

COMPARATOR

disabled

enabled

disabled

enabled

disabled

enabled

Table 7 AFC input selection

AFCH1 AFCH0

0

0

0

1

1

0

1

1

SELECT

AFC Channel 0; AFC0

AFC Channel 1; AFC1

AFC Channel 2; AFC2

reserved

handbook, full pagewidth

DP10/AFC0

DP11/AFC1

DP12/AFC2

AFC

ANALOG

SELECTOR

(DP10 to DP12)

EN0

EN1

EN2

Internal bus

COMPARATOR

EN

‘MOV A, D20’

instruction

to read AFCCx bit

Channel selection AFCH1 AFCH0

ENABLE

SELECTOR

4-BIT D/A

AFCE0 AFCE1 AFCE2

AFC function enable

selection

AFCV3 AFCV2 AFCV1 AFCV0

MED185

AFC value selection

1995 Jun 15

Fig.11 AFC circuit.

14

Share Link: