Storage Space - Loewe Q2500B Serviceanleitung

Technology of Q 2500 colour TV set
SAA4955HL block diagram
Y0-7 C0-3
WE
Input buffer
Daten
Write register
Memory
256k x 12 bit
Read register
Daten
Output buffer
Y0-7
C0-3
The picture memory in SAA 4979 is for the
actual 100 Hz function in the circuit, whereas
picture memories 2 and 3 I 2451/ I 2461 facili-
tate noise suppression, the suppression of line
quivering, interpolation and a full line freeze
frame by a delay of 1 half picture.
Data writing and reading for the two memories
take place completely independently of each
other.
Inputting and outputting for a single memory is
also separately controlled. Data is therefore
written to one area of the memory, whilst it is
read from another area.
Document Q 2500
IE
Write controller
Data
Adress block
write
read
refresh
Daten
Read register
SWCK
RE
RSTR
OE
4.4.1

Storage space

The IC is organised into in 256 k words each
of 12 bit. Two independent clock signals for
writing and reading allow these functions to be
carried out concurrently and independently.
A total of 3 072 000 bits can be stored, which
corresponds to a little more than one half pic-
ture.
This comprises the following:
Sampling rate 16 MHz at a line frequency of
15.625 kHz
16 MHz
-----------------
15.625 kHz
As the synchronous pulse and the front and
rear black shoulder are not required, there are
832 sampling values per line for the actual
picture signal. A sample value corresponds to
one displayed pixel on the screen.
The sampling gap is not required in the verti-
cal direction either. There are therefore 290
lines per half picture.
832 pixels x 290 lines = 241 280 pixels
Therefore for each half picture 241 280 pixels
must be stored. At a resolution of 8 bit Y and 4
bit chroma
241,280 pixels x 12 bit = 2,895,360 bit
are required for half picture storage capacity.
The 3 Mbit is sufficient for the separate, con-
tinual inputting and outputting of this function.
91
= 1024 sampling values
per line
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