ADVANCE INFORMATION
DDP 3310B
2.2.3. Fast-Blank Monitor
2.2.4. CRT Measurement and Control
The presence of external analog RGB sources can be
detected by means of a Fast-Blank monitor. The status
of the selected Fast-Blank input can be monitored via
an I2C register. There is a 2-bit information, giving
static and dynamic indication of a Fast-Blank signal.
The static bit is directly reading the Fast-Blank input
line, whereas the dynamic bit is reading the status of a
flip flop triggered by the negative edge of the Fast-
Blank signal.
The display processor is equipped with an 8/12-bit
PDM-ADC for all picture tube measuring purposes.
This MADC is connected to the SENSE input pin, the
input range is 0 to 1.6V.
Cutoff and white-drive current measurement are car-
ried out with 8-bit resolution during the vertical blank-
ing interval. The current range for cutoff measurement
is set by connecting the resistor R1 to the SENSE
input. Due to the fact of a 1:10 relation between cutoff
and white-drive current, the range select 2 output
(RSW2) becomes active for the white-drive measure-
ment and connects R3 in parallel to R1, thus determin-
ing the correct current range. During the active picture,
the MADC is used for the average beam current limiter
with a 12-bit resolution. Again, a different measure-
ment range is selected with active range select 1&2
outputs (RSW1&RSW2) connecting R2 in parallel to
R3 and R1. See Fig. 2–10 and Fig. 2–11 for the corre-
sponding timing. These measurements are typically
done at the summation point of the picture tube cath-
ode currents.
With this monitor logic it is possible to detect if there is
an external RGB source active and if it is a full-screen
insertion or only a box. The monitor logic is connected
directly to the FBLIN1 or FBLIN2 pin. Selection is done
via I2C register.
FBFOH1 FBFOL1
FBPOL
FBPRIO
#
FBLIN1
Fast-
Blank
int
Another method uses two different current measure-
ments. The range switch 1 pin (RSW1) can be used as
a second Sense input, selectable by software. In this
case, the cutoff and white-drive currents are measured
as before at the SENSE input. The active picture mea-
surement can be done with the second Sense input
(RSW1). The signal may come (via a proper interface)
from the low end of the EHT coil (CRT anode current).
In this case, the resistor R2 in Fig. 2–10 has to be
removed.
Fast-
Blank
Monitor
Fast-
Blank
Selection
FBLIN2
#
FBFOH2 FBFOL2
FBMON
Fig. 2–9: Fast-Blank selection logic
Beam Current 2
Beam Current 1
SENSE
A
D
MADC
R2
R3
RSW1
RSW2
R1
Fig. 2–10: MADC range switch
Micronas
13
MICRONAS [ MICRONAS ]
