TLC34076_16 Datasheet, PDF (42/69 Pages) Texas Instruments – Video Interface Palette

calculated at a speed of (DOTCLK frequency)/2. During the vertical retrace activated by a falling edge on
the TLC34076 VSYNC input, the value in the temporary accumulator is transferred into the ones
accumulation register, and then the temporary accumulator is reset to 0. The ones-accumulation register
is updated only on the falling edge of VSYNC, not by any vertical sync pulses coded into the composite video
signal. Before the next frame scan begins, the TLC34076 automatically changes the value in bits D2 – D0
so that the ones accumulation performed during the next frame scan is for a different color byte (see the
screen integrity test state diagram of Figure 2–11). As long as the screen display remains fixed, the
ones-accumulation value for a particular color byte should not change; when it does, an error has occurred.
Since ones accumulation is calculated at DOTCLK/2 rate, there is uncertainty as to whether it starts its
accumulation on an odd or even pixel. Regardless of whether the accumulation is performed on odd or even
pixels, subsequent screens are accumulated starting at the same point every time, unless the part is reset
or the DOTCLK source changes.
2.12.4 Analog Test
An analog test compares the voltage amplitudes of the analog red-green-blue (RGB) outputs to each other
and to a 145-mV reference. This enables the MPU to determine whether the CRT monitor is connected to
the analog RGB outputs or not and whether the DACs are functional. To perform an analog test, bits D2
– D0 must be set to 111; D7 – D4 bits are set as shown in Table 2–13. Bit D3 contains the result of the analog
test. The bit coding for the analog comparison of bits D2 – D7 is shown in Table 2–14.
Table 2–13. Test Register Bit Definitions for Analog Test
BIT DEFINITION
READ/WRITE
D7: Red select
Read/Write
D6: Green select
Read/Write
D5: Blue select
Read/Write
D4: 145-mV reference select
Read/Write
D3: Result
Read
Table 2–14. Bit Coding for Analog Comparisons of Bits D7 – D4
D7 – D4
OPERATION
IF D3 = 1
IF D3 = 0
0000 Normal operation
Don’t care
Don’t care
1010 Red DAC compared to blue DAC
Red > blue
Red < blue
1001 Red DAC compared to 145-mV reference
Red > 145 mV
Red < 145 mV
0110 Green DAC compared to blue DAC
Green > blue
Green < blue
0101 Green DAC compared to 145-mV reference Green > 145 mV Green < 145 mV
NOTE 2: All the outputs have to be terminated to compare the voltage.
2–26