LNBS21

5/21

Figure 3: Typical Application Circuit

(*) Set to GND if not used

not implemented (see DiSEqC implementation note)

(***) IC2 is a ST Fettky, STS4DNFS30L, that includes both the schottky diode and the N-Channel MosFet, needed for the DC/DC converter,

in a So-8 package. It can be replaced by a schottky diode (STPS2L3A or similar) and a N-Channel MosFet (STN4NF03L or similar)

Data transmission from main µP to the LNBS21

bus interface, consisting of the two lines SDA and

SCL (pull-up resistors to positive supply voltage

must be externally connected).

DATA VALIDITY

As shown in fig. 1, the data on the SDA line must

be stable during the high period of the clock. The

HIGH and LOW state of the data line can only

change when the clock signal on the SCL line is

LOW.

START AND STOP CONDITIONS

As shown in fig.2 a start condition is a HIGH to

LOW transition of the SDA line while SCL is HIGH.

The stop condition is a LOW to HIGH transition of

the SDA line while SCL is HIGH. A STOP

conditions must be sent before each START

condition.

BYTE FORMAT

Every byte transferred to the SDA line must

contain 8 bits. Each byte must be followed by an

acknowledge bit. The MSB is transferred first.

ACKNOWLEDGE

The master (µP) puts a resistive HIGH level on the

SDA line during the acknowledge clock pulse (see

fig.

3).

The

peripheral

(LNBS21)

that

acknowledges has to pull-down (LOW) the SDA

line during the acknowledge clock pulse, so that

the SDA line is stable LOW during this clock pulse.

The peripheral which has been addressed has to

generate an acknowledge after the reception of

each byte, otherwise the SDA line remains at the

HIGH level during the ninth clock pulse time. In

this case the master transmitter can generate the

STOP information in order to abort the transfer.

The LNBS21 won't generate the acknowledge if

threshold (6.7V typ.).

TRANSMISSION WITHOUT ACKNOWLEDGE

Avoiding to detect the acknowledge of the

LNBS21, the µP can use a simpler transmission:

270µH

15 ohm

see Note 2

LNBS21

Vup

Gate

Vin

12V

L1=22µH

Sense

C2

220µF

Vcc

LT1

Master STB

Vo

LT2

DETIN

(Note 1)

C8

10nF

to LNB

SDA

SCL

DSQOUT

DSQIN(Note 1)

ADDRESS

Byp

C5

470nF

GND

EXTM

C6

10nF

0.1

Ω

Ω

Ω

Ω

C3

470nF

Ceramic

D1 1N4001

C1

220µF

C4

470nF

Ceramic

D2

BAT43

C7

10nF

STS4DNFS30L

IC2

(Note 3)

IC1

(Note 4)