BUF12840_15 Datasheet, PDF (11/31 Pages) Texas Instruments – Programmable Gamma-Voltage Generator

BUF12840
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POWER-ON RESET (POR) AUTO READ
FUNCTION
Figure 14 depicts the BUF12840 POR Master Mode
auto read function and timing. The BUF12840 makes
the first attempt to read the external EEPROM 5ms
after the POR (power-on reset) condition is met, as
shown in Figure 13. Following the initial 5ms wait
period, the BUF12840 queries the EEPROM with a
digital word that includes an EEPROM address and
acknowledge request. If communication with the
EEPROM is established, the download finishes in
10ms.
However, if the first read attempt is not successful,
the BUF12840 waits for 1ms and then tries to start
the download again. This process repeats itself until a
successful acknowledge from the EEPROM is
detected or until 10 read attempts have been made. If
at any time during this process the BUF12840 does
detect a successful acknowledge from the EEPROM
and the EN pin is properly set, the BUF12840 initiates
the upload and reads the contents of the EEPROM,
which takes approximately 10ms to complete. The
DAC outputpower-on reset value is 0V. The state of
V_S (analog supply voltage) does not affect POR or
the auto read function.
V_SD
SBOS519A – OCTOBER 2010 – REVISED JULY 2011
Immediately after power up, all DAC outputs are set
to 0V. During the auto-read function, values are
written into the DAC registers as they are being read
from the EEPROM. Once the auto-read function is
complete, all values are simultaneously loaded from
the DAC registers to the DAC outputs. Therefore, all
values change together. This action is performed
regardless of the state of the LD pin and occurs by
default after auto-read is completed.
Once the information is downloaded from the
EEPROM, the BUF12840 automatically goes into
slave mode, where all slave mode operations are
supported. The BUF12840 remains in slave mode
until another POR, GCR (general-call reset), or RA
(read again) condition is met.
The EN pin should be set to a high level within 15ms
of crossing the POR condition. If the EN pin active
high state is not detected during the first 10 query
attempts, the BUF12840 automatically enters slave
mode. If the master mode auto read function must be
terminated at any time during the auto read process,
the EN pin can be set to a low '0' level that forces the
BUF12840 into slave mode and the automatic
download process to stop. If an EEPROM
acknowledge is not detected during the possible 10
read attempts, the BUF12840 automatically goes into
slave mode following the tenth read attempt. Note
that the analog power, V_S, does not need to be on
during any interface communication.
POR (1.1V)
t_OFF ³ 100ms
t_F (min) ³ 500ms
Figure 13. POR
t_R (min) ³ 10ms
Copyright © 2010–2011, Texas Instruments Incorporated
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