TLC34076_16 Datasheet, PDF (41/69 Pages) Texas Instruments – Video Interface Palette

ID Code
011
RD
RESET
000
RD
Red
Red
010 _Blue
100
Blue
RD
110
RD
111
RD
RD
001 _Green
RD
RD
101 _Green
DAC ANALOG TEST
DATA FLOW CHECK
SCREEN INTEGRITY TEST
Figure 2–11. Test-Register Control-Word State Diagrams
2.12.1 Frame-Buffer Data Flow Test
The TLC34076 provides a means to check all the data entering each DAC but before the output MUX 8/6
shift. When accessing these color channels, the data entering the DACs should be kept constant for the
entire MPU read cycle. This can be done either by slowing down the dot clock or ensuring that the data is
constant for a sufficiently long series of pixels. The value read is the data stored in the color palette location
addressed by the data in the input MUX. The read operation causes a post-increment to point to the next
color channel, and the post-increment of blue wraps back to red as shown in the state diagram of Figure
2–11. For example, when bits D2 – D0 are written as 001, then three successive reads are performed, and
the values read out are green, blue, and red in this sequence.
2.12.2 Identification (ID) Code
The ID code can be used as a software identification for different versions. The ID code in the TLC34076
is static and can be read without consideration of the dot clock or video signals. To be user-friendly, the read
post-increment applies to the ID register as well. However, when the state machine goes into the color
channel, it does not return to the ID code unless the user writes 011 (binary) to bits D2, D1, and D0 again.
If the test register was first written as 011 (binary) in bits D2, D1, and D0, then, when six successive reads
are performed, the first value read is the ID, and the last value read is the green.
The ID value defined for the TLC34076 is 76 (hex).
2.12.3 Ones-Accumulation Screen Integrity Test
A technique called ones accumulation can detect errors in fixed screen displays. This type of error detection
is useful for system checkout and field diagnostics.
Each of the 256 24-bit words in the TLC34076 internal color palette RAM is composed of three bytes, one
each for the red, green, and blue components of the word. When bits D2 – D0 are programmed with the
appropriate binary value (see subsection 2.12.4), the TLC34076 monitors the corresponding color byte that
is output by the color palette RAM. For example, when bits D2 – D0 are programmed with the value 100,
the TLC34076 monitors the red byte. As the current frame is scanned, for each color palette RAM word
accessed, the designated color byte is checked to see how many 1 bits it contains, and this number is added
to a temporary accumulator, the entire byte is checked, even when 6-bit mode is selected. For example,
when the designated color byte contains the value 41h (0100 0001), then the value 2 is added to the
temporary accumulator, as 41h contains two bits set at 1. This process is continued until an entire frame
has been scanned; the same color byte is monitored for the entire frame. The temporary accumulator
truncates any overflow above the value 255. Due to circuit speed limitations, the ones accumulation is
2–25