Public Version
Display Subsystem Functional Description
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Table 7-45. Analog TV Output Control (continued)
Register CONTROL.CONTROL_AVDACx [x=1, 2] Description
[17] AVDACx_COMP_EN
Full scale swing selection
0: High full-scale output swing: 1.3 V (default)
1: Low full-scale output swing: 0.88 V
[16] AVDACx_COMP_EN
Current reference selection
0: External current reference (set by external resistor connected to
cvideo1_rset pin) (default)
1: Internal current reference
CAUTION
Any change to the control register must be done only when the respective
VDAC is off.
High full-scale swing is the default mode. Low-swing mode does not comply
with the NTSC and PAL video standards. It must be used only for backward
compatibility to the OMAP3430.
7.4.7.8
Video DC/AC Coupled TV Load
The 10-bit video DAC stage supports both DC-coupled and AC-coupled TV loads. The
CONTROL.CONTROL_DEVCONF1[11] TVACEN bit is used to define which output coupling is used (0:
DC coupling; 1: AC coupling). This bit is the first one to be programed according to the TV load on the
PCB board.
NOTE:
When DC coupling is used, there is a 180-mV DC offset at the TVOUT output (cvideo1_out
for AVDAC1 and cvideo2_out for AVDAC2).
7.4.7.9
TV Detection/Disconnection Pulse Generation and Usage
7.4.7.9.1 TV Detection/Disconnection Pulse Generation
The TV detect block is an integral part of the video DAC stage.
NOTE:
•
The TV detection/disconnection feature is supported only for AVDAC1.
•
The TV disconnection feature is recommended to save power. The TV
detection/disconnection is operational only when video out is active. Therefore, to detect
cable connection automatically, it is necessary to periodically activate the video out to
test for cable presence.
This block compares the output of AVDAC1 (cvideo1_out) to a reference, to sense the condition of the
load. To operate, the TV detect requires two digital signals, TVACEN and TVDET. The TVACEN signal
indicates to both TVOUT buffer and the TV detect circuit if the load is AC or DC coupled to adjust
accordingly. To enable the detection of the load, the video encoder generates a negative TVDET pulse
aligned with the TV sync pulses. The operation of the circuit is based on the difference in voltage levels in
the output of the buffer depending on the load status. The TV detect block compares the output against a
couple of references and the result is latched at the start of every sync pulse. The status, given by the
TVINT output bit, is read later with the TVDET pulse rising edge. The TVINT signal of AVDAC1 is
internally connected to channel 1 of the GPIO2 module, mapped as the TV detector interruption.
The following registers are used to set the TV detection/disconnection pulse:
•
The DSS.
register defines which pixels are used to start and
stop the pulse inside their respective line.
1698
Display Subsystem
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated
Содержание OMAP36 Series
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