Mitsubishi DPLUS 74SB -BKA Service Manual page 132

I²C-bus autosync deflection controller for PC monitors
Table 3 Activation of protection mode
ACTIVATION
Low supply voltage at
pin10
Power dip, below 8.1 V
X-ray protection XRAY
(pin 2) triggered
HPLL2 (pin 30) externally
pulled to ground
When the protection mode is active, several pins of the
TDA4857 are forced into a defined state:
HDRV (horizontal driver output) is floating
BDRV (B+ control driver output) is floating
HUNLOCK (indicates, that the frequency-to-voltage con-
verter is out of lock) is floating (HIGH-level via external
pull-up resistor)
CLBL provides a continuous blanking signal
The capacitor at HPLL2 is discharged.
If the soft start procedure is activated via the I²C-bus, all of
these actions will be performed in a well defined sequence.
RESET
increase supply voltage;
reload registers;
2
soft start via I C-bus
reload registers;
2
soft start via I C-bus or via
supply voltage
reload registers;
2
soft start via I C-bus
release pin 30
Power dip recognition
In standby mode the I²C-bus will only answer with an
acknowledge, when data is sent to control register with
subaddress 1AH. This register contains the standby and
soft start control bit.
If the I²C-bus master transmits data to another register, an
aknowledge is given after the chip address and the
subaddress; an acknowledge is not given after the data.
This indicates that only in soft start mode data can be stored
into normal registers.
If the supply voltage dips under 8.1 V the TDA4857 leaves
normal operation mode and changes into standby mode.
The microcontroller can check this state by sending data
into a register with the subaddress 0XH. The acknowl-
edge will only be given on the data if the TDA4857 is ac-
tive.
Due to this behavior the start-up of the TDA4857 is de-
fined as follows. The first data that is transferred to the
TDA4857 must be sent to the control register with
subaddress 1AH. Any other subaddress will not lead to
an acknowledge. This is a limitation in checking the I²C-
busses of the monitor during start-up.
7-31
TDA4857