Sat Unit Control - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
As both the vertical and the RGB output stage
obtain their operating voltage from the diode
split transformer, this allows the entire c.r.t. to
be switched off and the power input in this
mode to be reduced. In normal operation pin
79 of the CCU is at L level and transistor Q
2951 is high resistance.
The c.r.t. is switched off when:
a) a timed recording for a video recorder is
being processed in the TV set.
b) on switch off using the remote control, if
previously, via the video menu, a recorder
has been set to record.
c) on switch off using the remote control, if
previously overplaying between the sock-
ets of the TV has been activated.
d) Radio – operation is activated (after 20
sec.).
In all these cases all other stages of the chas-
sis are fully operational. Except for d) the
sound in the MSP 3410 is switched off via the
I²C bus.

4.1.12 SAT unit control

Control of the Sat/TwinSat unit is implemented
by the CCU via the I²C-Bus 2.
The SAT unit VI used is also able to control
appropriately equipped switch boxes or LNCs
via DiSEqC Level 1 (Digital Satellite Equip-
ment Control). In this system pulse modulation
of the 22 kHz signals allows data to be ex-
changed between receiver and peripheral de-
vices. This means that the current different
LNC supply voltage switching information, 22
kHz and control function will be replaced and
simplified by separate control lines.
In the standard, a logical 1 is defined as 11
periods of 22 kHz signals (0.5 ms) followed by
a 1 ms pause (22 periods). The logical 0 is
represented in reverse, i.e. 22 oscillations (1
ms) and then a 0.5 ms pause (11 oscillations).
For this, each bit requires 1.5 ms for the trans-
fer, which corresponds to a maximum transfer
speed of 666 bits per second. After each
Document Q 2500
transferred telegram, there must be a pause
of at least 6 ms (132 periods).
Control is implemented according to the Sin-
gle Master - Single/Multi Slave principle. Mas-
ter is always the SAT receiver, and the exter-
nal components (LNC multiswitch, etc.) are
the slaves. Therefore, each communication
from the receiver is started and the external
components can only transfer data, after they
have been requested to do so by the master.
A command from the master contains a 1 byte
frame, a 1 byte address, a 1 byte command
and 1 or more bytes of data. The responses
consist of a 1 byte frame and 1 or more bytes
of data. Each byte is always followed by a
parity bit (P) for error checking.
The frame byte determines, whether the data
is sent by the master or the slave. The ad-
dress byte contains the information that de-
termines which peripheral module (switchbox,
LNC ....) is addressed. The command byte
determines which switching function is to be
implemented (selection LNC, level switching
....). In the data byte additional information can
be exchanged. There is still enough free
space in the DiSEqC command set for future
requirements. This means that the system has
built in futurability.
For the DiSEqC control the SDA 6000 has an
input and output respectively. Communication
with the SAT unit in the device is via a com-
mon line on connector W 1211, pin 7 on the
basic board and from there via W 250, pin 8
on the SAT unit.
Pin 90 of the CCU is used as an output for the
control of peripheral devices. The 22 kHz-
signal on the SAT unit is switched using the
H level. By switching between the L and
H level the 22 kHz is switched by the SAT unit
for the required period and a command is then
issued via the coaxial cable.
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