BUF08821 Datasheet, PDF (11/27 Pages) Texas Instruments – Programmable Gamma-Voltage Generator and VCOM Calibrator with Integrated Two-Bank Memory

www.ti.com ................................................................................................................................................. SBOS438C – AUGUST 2008 – REVISED AUGUST 2009
Parity Error Correction
The BUF08821 provides single-bit parity error
correction for data stored in the nonvolatile memory
to provide increased reliability of the nonvolatile
memory. If a single bit of nonvolatile memory for a
channel fails, the BUF08821 corrects for it and
updates the appropriate DAC with the intended value
when its memory is acquired.
If more than one bit of nonvolatile memory for a
channel fail, the BUF08821 does not correct for it,
and updates the appropriate DAC/V_COM with the
default value of 1000000000.
DIE_ID AND DIE_REV REGISTERS
The user can verify the presence of the BUF08821 in
the system by reading from address 111101. The
BUF08821A returns 0010001001110101 when read
at this address. The BUF08821B returns
0010001001111101 when read at this address.
The user can also determine the die revision of the
BUF08821 by reading register 111100. The
BUF08821 returns 0000000000000000 when a RevA
die is present. RevB would be designated by
0000000000000001, and so on.
READ/WRITE OPERATIONS
Read and write operations can be done for a single
DAC/V_COM or for multiple DACs/V_COM. Writing to a
DAC/V_COM register differs from writing to the
nonvolatile memory. Bits D15–D14 of the most
significant byte of data determines if data are written
to the DAC/V_COM register or the nonvolatile memory.
Read/Write: DAC/V_COM Register (volatile memory)
The BUF08821 is able to read from a single
DAC/V_COM, or multiple DACs/V_COM, or write to the
register of a single DAC/V_COM, or multiple DACs/V_COM
in a single communication transaction. DAC pointer
addresses begin with 000000 (which corresponds to
OUT1) through 000111 (which corresponds to
OUT8). Address 010010 is for V_COM.
For writes to multiple channels in a single transaction,
the register pointer increments directly from 000111
through 010010. This allows all eight gamma
channels plus the V_COM channel to be updated in one
transaction by sending nine words of data.
Write commands are performed by setting the
read/write bit LOW. Setting the read/write bit HIGH
performs a read transaction.
Writing: DAC/V_COM Register (Volatile Memory)
To write to a single DAC/V_COM register:
1. Send a START condition on the bus.
2. Send the device address and read/write bit =
LOW. The BUF08821 acknowledges this byte.
3. Send a DAC/V_COM pointer address byte. Set bit
D7 = 0 and D6 = 0. Bits D5–D0 are the
DAC/V_COM address. The BUF08821
acknowledges, stores, and returns data only from
these addresses:
– 000000 through 000111
– 010010
See Table 4 for valid DAC/V_COM addresses.
4. Send two bytes of data for the specified register.
Begin by sending the most significant byte first
(bits D15–D8, of which only bits D9 and D8 are
used, and bits D15–D14 must not be 01),
followed by the least significant byte (bits
D7–D0). The register is updated after receiving
the second byte.
5. Send a STOP or START condition on the bus.
The BUF08821 acknowledges each data byte. If the
master terminates communication early by sending a
STOP or START condition on the bus, the specified
register is not updated. Updating the DAC/V_COM
register is not the same as updating the DAC/V_COM
output voltage; see the Output Latch section.
Copyright © 2008–2009, Texas Instruments Incorporated
Product Folder Link(s): BUF08821
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