CP-520/520A/520F Service Manual available on one of the other CVBS inputs.In this condition the connections between the vision IF amplifier and the synchronisation circuit can be switched on and off by means of the VDX bit. The VDXEN bit must be set to �1� for this mode. The vertical synchronisation is realised by means of a divider circuit. 5.2.7 Horizontal and vertical drive The horizontal drive is switched on and off via the soft start/stop procedure. The soft start function is realised by means of variation of the TON of the horizontal drive pulses. During the soft-stop period the horizontal output frequency is doubled resulting in a reduction of the EHT so that the picture tube capacitance can easily be discharged. In addition the horizontal drive circuit has a �low-power start-up� function. The vertical ramp generator needs an external resistor and capacitor. For the vertical drive a differential output current is available. The outputs must be DC coupled to the vertical output stage. The IC has the following geometry control functions: n Vertical amplitude n Vertical slope n S-correction n Vertical shift n Vertical zoom n Vertical scroll n Vertical linearity correction. When required the linearity setting for the upper and lower part of the screen can have a different setting. n Horizontal shift n EW width n EW parabola width n EW upper and lower corner parabola correction n EW trapezium correction n Horizontal parallelogram and bow correction. When the East-West geometry function is not required (e.g. for 90 picture tubes) the EW output pin can be used for the connection of the AVL capacitor. This function is chosen by means of the AVLE bit. 5.2.8 Chroma, luminance and feature processing Someversionscontaina4H/2H(2D)adaptivePAL/NTSC comb filter. The comb filter is automatically activated when standard CVBS signals are received.A signal is considered as �standard signal� when a PAL or NTSC signal is identified and when the vertical divider is in the modes �standard narrow window� or �standard TV norm�.For non-standard signals and for SECAM signals the comb filter is bypassed and the signal is filtered by means of bandpass and trap filters. The chroma band-pass and trap circuits (including the SECAM cloche filter) are realised by means of internal filters and are tuned to the right frequency by comparing the tuning frequency with the reference frequency of the colour decoder.
