TLC34058 Datasheet, PDF (19/26 Pages) Texas Instruments – 256 × 24 COLOR PALETTE

PRINCIPLES OF OPERATION
TLC34058
256 × 24 COLOR PALETTE
SLAS050 – D3961, NOVEMBER 1991
test register
The test register allows the MPU to read the inputs to the DAC for diagnostic purposes. The MPU can write to
or read from this register at any time. This register is not initialized. Only the four least significant bits can be
written to, while all 8 bits can be read. Note that test register bit 0 corresponds to data bus line D0.
A function description of this register is presented in Table 8.
Table 8. Functional Description of Test Register
TR3–TR0
0100
0010
0001
1100
1010
1001
D4–D7
4 MSBs of blue data input
4 MSBs of green data input
4 MSBs of red data input
4 LSBs of blue data input
4 LSBs of green data input
4 LSBs of red data input
FUNCTION
MPU read or write D0 – D3
MPU read D0 – D7
To read the DAC inputs, the MPU must first load the test register’s four least significant bits. One of the test
register bits, b0 (red DAC), b1 (green DAC) or b2 (blue DAC), must be set high and the other two bits low. This
process determines whether the inputs to the red, green, or blue DAC will be read. The test register bit b3 must
be set high for reading the four most significant DAC inputs or low for reading the four least significant inputs.
The MPU then reads the test register while the test register’s four least significant bits contain the previously
written information. Note that either the device clock must be slowed down to the MPU cycle time or the same
pixel and overlay data must be continuously presented to the device during the entire MPU read cycle.
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