ST63156 datasheet(47/86 Pages) STMICROELECTRONICS

47 / 86 page

AFC A/D INPUT, KEYBOARD INPUTS

AND BANDSWITH OUTPUTS

The AFC macrocell contains an A/D comparator

with five levels at intervals of 1V from 1V to 5V. The

levels can all be lowered by 0.5V to effectively dou-

ble the resolution. This A/D can be used to perform

the AFC function. In addition this cell offers also a

keyboard input register of three bits used to per-

form a keyboard scan and 4 open-drain outputs

(able to withstand signals up to 12V) that can be

used to perform band switch function.

Figure 53. AFC, KBY Inputs Configuration Dia-

grams

Figure 54. BSW, DA, OUT1 Output Configu-

ration Diagram

A/D Comparator

The A/D used to perform the AFC function (when

high threshold is selected) has the following volt-

age levels: 1,2,3,4 and 5V. Bits 0-2 of AFC result

nary form (less than 1V is 000, greater than 5V is

101).

If the application requires a greater resolution, the

sensitivity can be doubled by clearing to zero bit 7 of

DA3 Data/Control register, address E3h (refer to

D/A description for additional information). In this

case all levels are shifted lower by 0.5V. If the two

results are now added within a software routine

then the A/D S-curve can be located within a resolu-

tion of 0.5V. The A/D input has high impedance able

to withstand up to 13V signals (input level toler-

ances

± 200mv absolute and ± 100mv relative to

5V).

AFC, Keyboard Inputs and Bandswitch Out-

puts Data/Control Registers

AFCR

AFC Result Register

(E4h, Read Only)

D7 D6 D5 D4 D3 D2 D1 D0

AD2-AD0 A/D = Conversion

Result

Unuse d

Figure 55. AFC Result Register

D7-D3. These bits are not used.

AD0-AD2. These bits store the real time conver-

sion of the value present on the AFC input pin. No

reset value.

ST63140,142,126,156

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