TLC34077 Datasheet, PDF (16/41 Pages) Texas Instruments – Video Interface Palette Data Manual

2.3.1 LCLK
Data is latched inside the device on the rising edge of LCLK, which is an internal programmable signal.
Therefore, LCLK must be set as a function of the pixel bus width and the number of bit planes. LCLK can
be selected as divisions of 1 or 2 of the dot clock. If LCLK is not used, the output can be switched off and
held low.
The trailing edge of VCLK is used internally by the TLC34077 to sample and latch the BLANK input. The
TLC34077 video blanking circuitry is designed with sufficient pipeline delay to allow the internal sampled
BLANK signal to align with the pipelined RGB data to the video DACs. The logic described above works in
situations where the LCLK period is shorter than, equal to, or longer than the VCLK period.
The default divide ratio for LCLK is 1:1, as used in Mode 0.
Depending on the frequency relationship between LCLK and VCLK, their phase relationship could be
critical. Please refer to Appendix C for a more detailed discussion.
2.3.2 VCLK
The VCLK frequency can be selected to be 1/1 or 1/2 of that of the dot clock, or it can be held at a high logic
level. The default condition is for VCLK to be held at a high logic level. VCLK is not used in VGA pass-through
mode.
VCLK is used by a GSP or custom-designed control logic to generate control signals (BLANK, HSYNC, and
VSYNC). As can be seen from Figure 2– 2, since the control signals are sampled by VCLK, it is obvious that
VCLK has to be enabled.
VCLK
BLANK
at Input Pin
LCLK
(Internal Signal
for Data Latch)
BLANK
(Internal Signal
Before DOTCLK
Pipeline Delay)
PIXEL DATA
at Input Pin
Latch Last Group
of Pixel Data
Latch First Group
of Pixel Data
Latch Last Group
of Pixel Data
Last Group of Pixel Data
1st
Group
G2rnodupG3rrodupG4rtohupG5rtohup
6th
Group
Figure 2–2. LCLK/VCLK Control Timing
2.4 Multiplexing Scheme
The TLC34077 offers a highly versatile multiplexing scheme as illustrated in Table 2–5. The on-chip
multiplexing allows the system to be reconfigured to different dilsplay modes without hardware modification.
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