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Service manual SC-150
-51-
5-3-20 EHT Compensation
The vertical waveform can be scaled according to the average beam current. This is used to compensate the effects of
electric high-tension changes due to beam current variations. EHT compensation for East/West deflection is done with
an offset corresponding to the average beam current.
5-3-21 Reset Function
Reset of all VDP functions is performed by the RESQ pin. When this pin becomes active, all internal registers and
counters are lost.
5-3-22 Standby and Power-On
The VDP does not have a standby mode. To disable all the analogue and digital video functions, it is necessary to
switch off the supplies for analogue front-end (VSUP AF ), analogue back-end (VSUP AB ) and digital circuitry
(VSUP D ).
5-4- Microcontroller
5-4-1 Introduction
The TV controller basically consists of the CPU, RAM, ROM, and a number of peripheral modules.
For instance:
– a memory banking module is included to allow access to more than 64 kB memory.
– a bootloader softwa re is included to allow in-system-downloading of external code to Flash memory via the I 2 C
interface.
The TV controller runs the complete software necessary to control a TV set. The software includes control of the audio,
video, OSD, and text processors on chip, as well, as control of external devices like tuner or stereo decoder.
Communication between the TV controller and external devices is done either via I 2 C bus interface or via program-
mable port pins. The TV Controller is clocked with f OSC = f XTAL /2.
5-4-2 CPU
The CPU is fully compatible to WDC’s W65C02 micro-processor. The processor has 8-bit registers/accumulator, an 8-
bit data bus, and a 16-bit address bus.