Philips Semiconductors
Product specification
I2C-bus autosync deflection controller for
PC monitors
TDA4841PS
I2C-BUS PROTOCOL
Data format
The format of data for the I2C-bus is given in Table 4.
Table 4 Data format
S(1)
SLAVE ADDRESS(2)
A(3)
SUBADDRESS(4)
A(3)
DATA(5)
A(3)
P(6)
Notes
1. S = START condition.
2. SLAVE ADDRESS (MAD) = 1000 1100.
3. A = acknowledge, generated by the slave. No acknowledge is given, if the supply voltage is below 8.2 V for start-up
and 8.0 V for shut-down procedure.
4. SUBADDRESS (SAD).
5. DATA byte. If more than 1 byte of DATA is transmitted, then no auto-increment of the significant subaddress is
performed.
6. P = STOP condition.
It should be noted that clock pulses according to the
400 kHz specification are accepted for 3.3 V and 5 V
applications (reference level = 1.8 V).
This mode should be used if many register values have to
be changed subsequently, i.e. during start-up, mode
change, etc., and while there is no picture visible on the
screen (blanked). The number of transmissions per
V-period is not limited.
Default register values after power-up are random.
All registers have to be preset via software before the soft
start is enabled.
Buffered mode
It should be noted that if register contents are changed
during the vertical scan, this might result in a visible
interference on the screen. The cause for this interference
is the abrupt change of picture geometry which takes effect
at random locations within the visible picture. To avoid this
kind of interference, at least the adjustment of some critical
geometry parameters should be synchronized with the
vertical flyback. The TDA4841PS offers a feature to
synchronize any I2C-bus adjustment with the internal
vertical flyback pulse. For this purpose the IC offers two
different modes for the handling of I2C-bus data:
The buffered mode is selected by setting the MSB of the
I2C-bus register subaddress to logic 1.
This mode is designed to avoid visible interferences on the
screen during the I2C-bus adjustments. This mode should
be used, if a single register has to be changed while the
picture is visible, so i.e. for user adjustments.
One received I2C-bus data byte is stored in an internal
8-bit buffer before it is passed to the DAC section. The first
internal vertical blanking pulse (VBL) after end of
transmission is used to synchronize the adjustment
change with the vertical flyback. So the actual change of
the picture size, position, geometry, etc. will take place
during the vertical flyback period, and will thus be invisible.
• Direct mode
• Buffered mode.
Direct mode
The IC gives acknowledge for chip address, subaddress
and data of a buffered transmission. Only one I2C-bus
transmission is accepted after each vertical blank. After
one buffered transmission, the IC gives no acknowledge
for further transmissions until next VBL pulse has
occurred. The buffered mode is disabled while the IC is in
standby mode.
The direct mode is selected by setting the MSB of the
I2C-bus register subaddress to logic 0.
Any I2C-bus command is executed immediately after it
was received, so the adjustment takes effect immediately
after the end of I2C-bus transmission.
1999 Oct 25
34
NXP [ NXP ]
