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Display Subsystem Basic Programming Model
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7.5
Display Subsystem Basic Programming Model
This section describes how to configure the display subsystem for the desired functionalities and also
describes the programming models of the display controller, the RFBI and the video encoder.
The main configuration scenarios are:
•
LCD panel support (bypass or RFBI mode)
Configure the RFBI module (only if in RFBI mode; otherwise, the default values must remain), and then
configure the display controller to the desired functionalities before the activities start.
•
TV set support
Configure the video encoder and then the display controller.
•
Both LCD panel support (bypass or RFBI mode) and TV set support
Configure the RFBI module (only if in RFBI mode; otherwise, leave the default values), configure the
video encoder, and then configure the display controller.
7.5.1 Display Subsystem Reset
The display subsystem can receive a software reset that is propagated through all of the submodules to
initialize the subsystem. The following procedure describes a possible sequence:
1. If the LCD is on, stop the LCD by setting the DSS.
[0] LCDENABLE bit to 0.
(a) Reset the frame done status bit by writing 1 in the DSS.
[0] FRAMEDONE bit.
(b) Wait until the DSS.
[0] FRAMEDONE bit is set to 1. This shows that the end of
frame has taken place and the LCD stop is complete.
2. To take the display subsystem out of reset, all clocks related to the display subsystem must be
enabled and the DPLL4 must be enabled. The following clocks must be enabled to take the display
subsystem out of reset:
•
PRCM.CM_FCLKEN_DSS[0] EN_DSS1 bit set to 1
•
PRCM.CM_FCLKEN_DSS[1] EN_DSS2 bit set to 1
•
PRCM.CM_FCLKEN_DSS[2] EN_TV bit set to 1
•
PRCM.CM_ICLKEN_DSS[0] EN_DSS bit set to 1
Once the clocks are enabled as shown, the display subsystem can be taken out of reset.
3. Write 1 in the DSS.
[1] SOFTRESET bit to apply the soft reset to the subsystem.
4. Read the DSS.
[0] RESETDONE bit. If this bit is 1, the reset sequence is complete;
otherwise, read this bit again (the reset sequence is not completed).
7.5.2 Display Subsystem Configuration Phase
The display subsystem configuration phase is important to configure the data flow for using the LCD panel
or the TV set. Use the following flow:
1. To configure the top level of the functional clock of the display controller clock, set the
DSS.
[0] DSS_CLK_SWITCH bit.
2. To configure the top level of the video encoder, set the DSS.
VENC_CLOCK_MODE bit and the DSS.
[3] VENC_CLOCK_X4 bit for TV set support.
3. To configure the top level of the DAC stage, set the DSS.
[4] DAC_DEMEN bit for TV
set support (if required).
4. Configure the RFBI module and/or the video encoder as needed.
5. Configure the display controller.
7.5.3 Display Controller Basic Programming Model
Some display controller registers are termed shadow registers, which are associated with the digital output
and/or the LCD output. A shadow register change has no direct effect on the configuration of the display
controller unless the DSS.
[5] GOLCD bit is set for the LCD output and/or the
[6] GODIGITAL bit is set for the digital output.
1706
Display Subsystem
SWPU177N – December 2009 – Revised November 2010
Copyright © 2009–2010, Texas Instruments Incorporated