Sram; Search Functions; Storage; Programme Recall - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
4.2.4

SRAM

Data that is necessary for the functioning of
the CCU is temporarily saved in the 64MBIT
DRAM I 2916. Owing to additional functions in
the EPG and DVB the internal RAM area in
the CCU is no longer sufficient to store all the
data required. Up to 3000 videotext pages are
stored in this DRAM.
4.2.5

Search functions

On implementing the search function by
pressing the appropriate button the SDA 6000
permits the SAA 4979, via the I²C bus, to out-
put permanent blank in the blank stages. In
this way the picture is sampled and using an-
other command from the MSP, the sound as
well.
The required frequency is communicated as a
whole number multiple of 62.5 kHz from the
SDA 6000 via the I²C bus to the tuning IC.
From the tuner each set oscillator frequency is
present as the actual value. It is sub-divided in
the IC and compared to a reference fre-
quency. The sub-multiple ratio is determined
by C 161.
Using internal UP and DOWN pulses the tun-
ing voltage is delayed until compatibility is
reachd. The PLL engages and communicates
this to the SDA6000 via the I²C bus. It then
requests the VPC via the I²C bus for the avail-
able standardised synchronous signals. If
synchronous pulses are present, the perma-
nent blank is lifted. In the event that there are
no synchronous signals, the SDA 6000 com-
municates to the tuning IC the next highest
sub-multiple and the tuning procedure begins
anew. The search procedure only stops when
a transmitter is found. The SDA 6000 deter-
mines this by querying the VPC about the
synchronous pulses present.
During the search procedure the channels are
searched in ascending order within the se-
lected standard. For the PAL B/G, SECAM
East, NTSC Europa and SECAM L standards,
cable channels are also searched.
Document Q 2500
On transfer from one FS band to another, the
corresponding band switching information is
automatically switched at the same time. De-
pending on the device settings changing of
standards is carried out either automatically or
manually.
If no transmitter is detected in the selected
channel on the normal frequency, the channel
is searched from its lower limit in 1 MHz steps.
If a transmitter is still not found, the system
jumps to the next highest channel.
4.2.6

Storage

If a channel has been found and the correct
standard set by the search procedure or direct
input of a channel, it can be saved to any pro-
gramme location between 00 and 220. In ad-
dition, all tuning and switching information is
written to the EAROM via the I²C bus.
4.2.7

Programme recall

For programme recall the required programme
number is input to the SDA 6000 via the re-
mote control. Via the I²C bus it requests the
EAROM to communicate the details of this
storage location (division ratio, fine tuning, FS
standard). This Information is passed via the
I²C bus from the memory to the SDA 6000,
which then passes it to the tuning IC in the
tuner. The IC sets the band switching outputs
to the required band and required standard
and moves the tuner oscillator to the allocated
frequency. The fine-tuning value is also con-
sidered with respect to the oscillator frequency
and corrected by the AFC. The tuning remains
on the required frequency, even when no
transmitter is available.
76 © Loewe ProCollege