TLC34076 Datasheet, PDF (32/68 Pages) Texas Instruments – Video Interface Palette

2.4.6 Read Masking
The read mask register enables or disables a pixel address bit from addressing the color palette RAM. Each
palette address bit is logically ANDed with the corresponding bit from the read mask register before
addressing the palette. This function is performed after the addition of the page register bits and, therefore,
a zeroing of the read mask results in one unique palette location (location 0) and is not affected by the palette
page register contents.
Note also that the read mask can zero the overlay data in the true-color modes. This is a handy way to
disable the overlay (enable true-color data to the DACs) for a whole screen.
2.5 Reset
There are three ways to reset the TLC34076:
• Power-on reset
• Hardware reset
• Software reset
2.5.1 Power-On Reset
There is a power-on reset (POR) circuit built into the TLC34076. This POR works at power-on only. Even
though this circuitry is provided, it is still recommended for the user to design a hardware reset circuit to
ensure the reset condition after power-up as described in subsection 2.5.2.
Once the voltage is stabilized, the default condition for all registers is the VGA mode. When the TLC34076
is reset, the SCLK and VCLK counters are reset as well (see Section 2.3 and subsection 2.5.4).
2.5.2 Hardware Reset
The TLC34076 resets whenever RS3 – RS0 = HHHH and a rising edge occurs on WR input. Resetting of
the TLC34076 is most reliable when many rising WR edges occur during the time RS=HHHH. This scheme
(bursting WR strobes until the power supply voltage stabilizes) is suggested at power up when a hardware
reset approach is used.
The default reset condition is VGA mode, and the values for each register are shown in subsection 2.5.4.
Also when the TLC34076 is reset, the SCLK and VCLK counters are reset (see Section 2.3).
2.5.3 Software Reset
Whenever the mux control register is set for VGA pass-through mode after power up, all registers are
initialized accordingly. Since VGA pass-through mode is the default condition at power up and hardware
reset, the act of selecting the VGA pass-through mode through programming the mux control register is
viewed as a software reset. Therefore, whenever mux control register bits 5 – 0 are set to 2Dh, the
TLC34076 initiates a software reset. This also resets the SCLK and VCLK counters (see Section 2.3). This
is referred to as a software reset, since it is typically initiated by software, unlike POR or hardware resets.
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