Technology of Q 2500 colour TV set

Technology of Q 2500 colour TV setSAA4955HL block diagramY0-7 C0-3WERSTWSWCKIEInput bufferWrite controller4.4.1 Storage spaceThe IC is organised into in 256 k words eachof 12 bit. Two independent clock signals forwriting and reading allow these functions to becarried out concurrently and independently.DatenDatenOutput bufferY0-7C0-3Write registerDataMemory256k x 12 bitDatenRead registerOEAdress blockwritereadrefreshRead registerRE SWCKRSTRA total of 3 072 000 bits can be stored, whichcorresponds to a little more than one half picture.This comprises the following:Sampling rate 16 MHz at a line frequency of15.625 kHz16 MHz----------------- = 1024 sampling values15.625 kHz per lineAs the synchronous pulse and the front andrear black shoulder are not required, there are832 sampling values per line for the actualpicture signal. A sample value corresponds toone displayed pixel on the screen.The sampling gap is not required in the verticaldirection either. There are therefore 290lines per half picture.The picture memory in SAA 4979 is for theactual 100 Hz function in the circuit, whereaspicture memories 2 and 3 I 2451/ I 2461 facilitatenoise suppression, the suppression of linequivering, interpolation and a full line freezeframe by a delay of 1 half picture.Data writing and reading for the two memoriestake place completely independently of eachother.Inputting and outputting for a single memory isalso separately controlled. Data is thereforewritten to one area of the memory, whilst it isread from another area.832 pixels x 290 lines = 241 280 pixelsTherefore for each half picture 241 280 pixelsmust be stored. At a resolution of 8 bit Y and 4bit chroma241,280 pixels x 12 bit = 2,895,360 bitare required for half picture storage capacity.The 3 Mbit is sufficient for the separate, continualinputting and outputting of this function.Document Q 2500 91 © Loewe ProCollege