PCA84C646 Philips Semiconductors, PCA84C646 Datasheet - Page 14

• Manufacturer Part Number: PCA84C646
• Description: Microcontrollers for TV tuning control and OSD applications
• Manufacturer: Philips Semiconductors

Philips Semiconductors
8
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 V
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 s but
less than 9 s. It is recommended to add a NOP instruction
between the instruction which changes V
selection and the instruction which reads the AFCC bit
(compare bit).
1995 Jun 15
handbook, full pagewidth
Microcontrollers for TV tuning
control and OSD applications
AFC INPUT
DP10/AFC0
DP11/AFC1
DP12/AFC2
Channel selection
DD
and V
AFCE0
AFC function enable
SS
AFCH1
(controlled by bits
SELECTOR
selection
AFCE1
ANALOG
AFC
AFCH0
ref
or channel
AFCE2
Fig.11 AFC circuit.
SELECTOR
ENABLE
14
If the compare bit:
Table 6 Selection of pin function DP1i/AFCi (i = 0, 1, 2)
Table 7 AFC input selection
AFCH1 AFCH0
AFCE2
AFCE1
AFCE0
AFCC = 0, then the AFC voltage < V
AFCC = 1, then the AFC voltage > V
BIT
AFCV3
0
0
1
1
EN0
VALUE
AFC value selection
AFCV2
COMPARATOR
(DP10 to DP12)
0
1
0
1
1
0
1
0
1
0
4-BIT D/A
PCA84C646; PCA84C846
EN1
EN
AFCV1
PIN FUNCTION
EN2
DP12
AFC2
AFC1
DP10
AFC0
DP11
AFC Channel 0; AFC0
AFC Channel 1; AFC1
AFC Channel 2; AFC2
AFCV0
to read AFCCx bit
Preliminary specification
SELECT
reserved
Internal bus
‘MOV A, D20’
MED185
instruction
ref
ref
COMPARATOR
.
.
disabled
disabled
disabled
enabled
enabled
enabled