ViewSonic E96f+SB-1, Service Manual

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x-ray protection
The x-ray ptotection(pin22) input XRAY provides a voltage detector with a precise voltage input for X-ray
protection .If the input voltage at XRAY exceeds the upper threshold for 150us to 300us,the system is forced to shut down
by switching off vertical,H-and B-drive signals.There are two different ways to handle the system in case of XRAY
occurrence:
1. If the xray latch enable bit UCXRAY[2] was set to “0” during startup the system will shut down without any interference
of the uC.The deflection controller is set to ldle mode.Restart of the system only possible due to seitching power off/power
on.
2. If register bit UCXRAY[2] was set to “1”,micro controller interaction is allowed .If the micro controller doesn’t interrupt
the system,the system will shut down to ldle mode.For any interaction of the micro controller the XRAY occurrence has to
be acknowledged by the micro controller by clearing the bit SY-STATUS[2].The micro controller take over the control of
the handling via software.The actual xray pin status can be read through bit SY-STATUS[1].
Quartz Oscillator(pin45,pin46)
The quartz oscillator circuit is available on pins XTAL1(input) and XTAL2(output) and works together with an external
48MHz 3
rd
overtone quartz.As a result the quartz oscillator is always running on 48MHz.Other quartz crystal frequencies
than 48 MHz cannot be used.External capacitors on XTAL1 and XTAL2 are not allowed.
B+ Control Function Block
The B+control block of the SAA4849 has the same behaviour as the TDA4856 with adapted threshol voltages.The
circuit allows the user to choose the trigger edge of the HDRV signal and the polarity of the output stage via I
2
C-Bus.
The B+ control function block of the SAA4849 consists of an Operational Transconductance Amplifier(OTA), a
voltage comparator,a flip-flop and a discharge circuit. This configuration allows easy application for different B+ control
concepts.
HPLL
The horizontal part contains a PLL,which works over the full frequency range from 25kHz to 140 kHz.This range can be
reduced by a ower and an upper frequency limit(Write Once Registers HPMAX and HPMIN).Via I
2
C bus the number of
48MHz clock cycles is sent through the register.The slewing speed during mode change is also programmable in a write once
register (HSLEW)
After the clocks for the HPLL are switched on,the HPLL starts with a fixed freerunning frequency of 60 kHz.The
H-drive pulses are not active and the start up procedure is inhibited.The default setting of register bit HCONTROL [0] will
cause the HPLL to slew ,not switch.to the freerunning frequency defined in the I
2
C register HPFREE( the default value is also
60 kHz).Independent on H-syncs which are possibly present.the HPLL will slew to that freerunning frequency.To achieve an
always defined starting point for the startup procedure,this procedure cannot be interrupted.
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