Display Freeze
9-37
Figure 9.18 Freeze Operation Timing
The Freeze Mode bits are sampled at the field boundaries. However, only
freeze requests issued before the first field in the frame are applied to
the frame. That is, a freeze request issued during the first field is applied
to the next frame. The return to normal request, however, is honored at
the next field.
Note:
Freezing for an odd number of field times causes a field
inversion. A field inversion is defined as displaying the top
field of a frame during an even field time and the bottom
field during an odd field time.
The host can detect the inversion condition by reading the First Field and
Top/Not Bottom Field bits in Register 275 (
page 4-62
). If they are at
opposite states, the fields are inverted. A single Freeze Last Field
request can correct the inversion. If the host sets the Automatic Field
Inversion Correction bit in Register 279 (
page 4-65
) and field inversion is
detected by the Display Controller, it displays the next frame starting at
display line two in the frame store.
The First Field bit in Register 275 (
page 4-62
) and Last Field bit in
Register 276 can be monitored by the host to determine which field in
the frame is currently being displayed. When both bits are cleared, a
middle field is being displayed as in pulldown or freeze modes.
O
E
O
E
O
E
O
E
T0
B0
T1
B1
T2
B2
T3
B3
Odd/Even
Normal Sequence
Freeze Frame
T0
B0
T1
B1
T1f
B1f
Freeze 1st Field
T0
B0
T1
T1f
T1f
& Hold
Freeze Last
T0
B0
T1
B1
B1f
B1f
B1f
Field
T1
T1f
T1
T2
T2
T2
Freeze Mode
Freeze Active
Normal
Normal