NEC uPD72257, Preliminary User'S Manual

Page: 95 / 343

4.5.3 Video Input control
The Video Input module control register SYSVIEN provides control bits to en- and
disable the Video Input module and to active on-chip loop-back functions.
4.5.3.1 Video Input enable
Prior using the Video Input module it has to be enabled. This is done by
• SYSVIEN.VIEN = 0: Video Input module disabled
• SYSVIEN.VIEN = 1: Video Input module enabled
After release of RESET SYSVIEN.VIEN is set o "0", thus the Video Input module
is disabled.
Notes
1. SYSVIEN.VIEN = 1 does not start capturing of video data. This is done by
setting VInCONTROL.CAPEN = 1 in the Video Input module.
2. If the Video Input module is disabled by SYSVIEN.VIEN = 0 all Video Input
registers can be accessed, but writing to the registers is ignored and reading
returns undefined values.
Caution
Disabling the Video Input module by SYSVIEN.VIEN = 0 requires particular
attention, as a special sequence must be applied. Refer to the section
"Start and
stop of video capturing" .
4.5.3.2 Video Input source selection
For testing and evaluation purposes the graphics controllers provide a loop-back
mode, that allows to capture the video data output from the Video Output module
by the Video Input module without external connections.
The Video Input source is selected by
• SYSVIEN.VISEL[1:0] = 00
B
: Video Input module signals are fixed to
low levels, i.e. no capturing
• SYSVIEN.VISEL[1:0] = 01
B
: Video Input module captures data from
the external interface (normal Video Input function)
• SYSVIEN.VISEL[1:0] = 10
B
: Video Input module captures data from
Video Output 0 (loop-back mode)
• SYSVIEN.VISEL[1:0] = 11
B
: Video Input module captures data from
Video Output 1 (loop-back mode)
Note After reset SYSVIEN.VISEL[1:0] is "00
B
", thus no data is supplied to the Video
Input. Prior using the Video Input module you must select the desired source
signals.
System Controller Chapter 4
Preliminary User's Manual S19203EE1V3UM00
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