Voltage References

Excess Peak Beam Current - A voltage threshold is set on
the beam current feedback on Pin 20, which is also used for
the RGB output loops for current sampling. When the
threshold is reached the flag is set, indicating too high a peak
beam current which may be in only a part of the screen. The
response of the MCU might be to reduce the contrast of the
Flag reading may be done at any time during a field.
However, writing to the MC44001 must be restricted to
certain times. If writing of new data is done during the
middle of a field, a disturbance will be seen on the screen,
particularly for the four user controls. While writing during
the vertical interval may appear to be the obvious solution
for this, there is a limited time available due to the contrast
control function which is carried out with RGB sampling
MC44001
READING AND WRITING TO THE MC44001
Flags From Chroma 4
Table 5. System Identification
picture. This flag together with the excess average beam flag
already described perform the function of beam limiting. The
exact way in which this is handled is left to the discretion of the
user who will have their own requirements, which may be
incorporated by the way in which the software is written.
loops during this interval. Writing during this particular time
can cause the sampling loops to become unstable.
The time available for writing new data is approximately
1.2 ms from the beginning of the field flyback pulse to the
beginning of the RGB sampling. It is only the third by1e
(data byte) which is restricted to this time interval. The first
two bytes may be sent previous to this, or also during
this time.