LNBEH21

9/22

VOM bit and TEN/VSEL pin functions with OM=1 (13/18V Control Word mode).

- When OM=1, the TEN/VSEL controls the 13/18V output voltage level. The usage of the TEN/VSEL

pin in combination with the VOM bit allows the 13/18V Control Word Communication (see block diagram

on page 1). The TEN/VSEL is a TTL control logic pin.

- in 13/18V Control Word Communication mode, the VOM bit does not control the LNB output voltage but

pin.

COMMUNICATION MODE IMPLEMENTATION

When OM=0, the LNBEH21 is suitable both for DiSEqC 2.0 and for unidirectional DiSEqC 1.x

applications.

The bi-directional DiSEqC 2.0 protocol implementation is allowed by an easy PWK modulation/

demodulation of the 22KHz carrier. The PWK data are exchanged between the LNBEH21 and the main

µP, using logic levels that are compatible with both 3.3 and 5V microcontrollers. This data exchange is

made through two dedicated pins, TEN/VSEL (when OM=0) and DSQOUT, in order to maintain the timing

relationships between the PWK data and the PWK modulation as accurate as possible. These two pins

should be directly connected to two I/O pins of the µP, thus leaving to the resident firmware the task of

encoding and decoding the PWK data in accordance to the DiSEqC protocol. The fully bi-directional

AC coupled to the DiSEqC TM bus and the extracted PWK data are available on the DSQOUT pin biased

with a pull-up resistor to a fixed voltage (see Fig. 7 and 8).

Full compliance of the system to the specification is not implied by the bare use of the LNBEH21; the

system designer should also take in consideration that, to comply to the bi-directional DiSEqC TM 2.0 bus

hardware requirements, an output R-L filter is needed. In order to help the system designer to avoid any

distortion during the 22KHz tone transmission, due to the output R-L impedance, the LNBEH21 is

to be used when the tone is received (see DiSEqC 2.0 typical application circuit). This allows the 22KHz

tone to pass without any losses due to the R-L filter.

Unidirectional DiSEqC 1.x and non-DiSEqC systems normally don't need the output R-L termination, and

application circuit). There is also no need of Tone Decoding, thus DETIN and DSQOUT pins can be left

always TTX=1.

When In DiSEqC mode, the Output Voltage level (13.1V,14.1V,19.5V,20.5V) is selected only by the VOM

detailed logic combination and corresponding function description).