BUF08821 Datasheet, PDF (13/27 Pages) Texas Instruments – Programmable Gamma-Voltage Generator and VCOM Calibrator with Integrated Two-Bank Memory

www.ti.com ................................................................................................................................................. SBOS438C – AUGUST 2008 – REVISED AUGUST 2009
Communication may be terminated by sending a
premature STOP or START condition on the bus, or
by not sending the acknowledge bit. The reading of
registers DieID, DieRev, and MaxBank is not
supported in this mode of operation (they must be
read using the single register read method).
The register pointer increments directly from 000111
through 010010 to allow all eight gamma channels
plus the V_COM channel to be updated in one
transaction.
Write: Nonvolatile Memory for the DAC Register
The BUF08821 is able to write to the nonvolatile
memory of a single DAC/V_COM in a single
communication transaction. In contrast to the
BUF20820, writing to multiple nonvolatile memory
words in a single transaction is not supported. Valid
DAC/V_COM pointer addresses begin with 000000
(which corresponds to OUT1) through 000111 (which
corresponds to OUT8). Address 010010 is for V_COM.
When programming the nonvolatile memory, the
analog supply voltage must be between 9V and 20V.
Write commands are performed by setting the
read/write bit low.
To write to a single nonvolatile register:
1. Send a START condition on the bus.
2. Send the device address and read/write bit =
LOW. The BUF08821 acknowledges this byte.
The BUF08821 acknowledges, stores, and
returns data only from these addresses:
– 000000 through 000111
– 010010
See Table 4 for DAC/V_COM addresses.
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.
4. Send two bytes of data for the nonvolatile register
of the specified DAC/V_COM. Begin by sending the
most significant byte first (bits D15–D8, of which
only bits D9 and D8 are data bits, and bits
D15–D14 must be 01), followed by the least
significant byte (bits D7–D0). The register is
updated after receiving the second byte.
5. Send a STOP 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
nonvolatile register is not updated. Writing a
nonvolatile register also updates the DAC/V_COM
register and output voltage.
The DAC/V_COM register and DAC/V_COM output voltage
are updated immediately, while the programming of
the nonvolatile memory takes up to 250μs. Once a
nonvolatile register write command has been issued,
no communication with the BUF08821 should take
place for at least 250μs. Writing or reading over the
serial interface while the nonvolatile memory is being
written jeopardizes the integrity of the data being
stored.
Read: Nonvolatile Memory for the DAC Register
To read the data present in nonvolatile register for a
particular DAC/V_COM channel, the master must first
issue a general acquire command, or a single acquire
command with the appropriate DAC/V_COM channel
chosen. This action updates both the DAC/V_COM
register(s) and DAC/V_COM output voltage(s). The
master may then read from the appropriate
DAC/V_COM register as described earlier.
Table 4. DAC Register Pointer Addresses
DAC REGISTER
OUT1
OUT2
OUT3
OUT4
OUT5
OUT6
OUT7
OUT8
V_COM
OTHER REGISTER
Die_Rev
Die_ID
MaxBank
POINTER ADDRESS
000000
000001
000010
000011
000100
000101
000110
000111
010010
POINTER ADDRESS
111100
111101
111111
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