11
FN8167.3
July 24, 2014
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Nonvolatile Write Acknowledge Polling
After a nonvolatile write command sequence is correctly
issued (including the final STOP condition), the X9252
initiates an internal high voltage write cycle. This cycle
typically requires 5ms. During this time, any Read or Write
command is ignored by the X9252. Write Acknowledge
Polling is used to determine whether a high voltage write
cycle is completed.
During acknowledge polling, the master first issues a START
condition followed by a Slave Address Byte. The Slave
Address Byte contains the X9252’s Device Type Identifier
and Device Address. The LSB of the Slave Address (R/W
)
can be set to either 1 or 0 in this case. If the device is busy
within the high voltage cycle, then no ACK is returned. If the
high voltage cycle is completed, an ACK is returned and the
master can then proceed with a new Read or Write operation
(see Figure 5).
2-Wire Serial Interface Operation
X9252 Digital Potentiometer Register Organization
Refer to the “Functional Diagram” on page 2. There are four
Digitally Controlled Potentiometers, referred to as DCPi,
i = 0, 1, 2, 3. Each potentiometer has one volatile Wiper
Control Register (WCR) with the corresponding number,
WCRi, i = 0, 1, 2, 3. Each potentiometer also has four
nonvolatile registers to store wiper position or general data,
these are numbered DRi0, DRi1, DRi2 and DRi3,
i = 0, 1, 2, 3.
The registers are organized in five pages of four, with one
page consisting of the WCRi (i = 0 to 3), a second page
containing the DRi0 (i = 0 to 3), a third page containing the
DRi1, and so forth. These pages can be written to four bytes
at time. In this manner all four potentiometer WCRs can be
updated in a single serial write (see “
Page Write Operation”
on page 14), as well as all four registers of a given page in
the DR array.
The unique feature of the X9252 device is that writing or
reading to a Data Register of a given DCP automatically
updates/moves the WCR of that DCP with the content of the
DR. In this manner data can be moved from a particular DCP
register to that DCP’s WCR just by performing a 2-wire read
operation. Simultaneously, that data byte can be utilized by
the host.
Status Register Organization
The Status Register (SR) is used in read and write
operations to select the appropriate DCP register. Before
any DCP register can be accessed, the SR must be set to
the correct value. It is accessed by setting the Address Byte
to 07h (see Table 3
). Do this by Writing the Slave Address
followed by a Byte Address of 07h. The SR is volatile and
defaults to 00h on power-up. It is an 8-bit register containing
three control bits in the 3 LSBs as follows:
Bits DRSel1 and DRSel0 determine which Data Register of a
DCP is selected for a given operation. NVEnable is used to
select the volatile WCR if “0”, and one of the nonvolatile
DCP registers if “1”. Table 2
shows this register organization.
“Store” operations using the Up/Down interface require that
bits DRSel1 and DRSel0 are set to “0”.
ACK RETURNED?
ISSUE SLAVE
ADDRESS BYTE
(READ OR WRITE)
BYTE LOAD COMPLETED BY ISSUING
STOP. ENTER ACK POLLING
ISSUE STOP
ISSUE START
NO
YES
NO
CONTINUE NORMAL READ OR
WRITE COMMAND SEQUENCE
PROCEED
YES
COMPLETE. CONTINUE COMMAND
SEQUENCE.
HIGH VOLTAGE
ISSUE STOP
FIGURE 5. ACKNOWLEDGE POLLING SEQUENCE
76543 2 1 0
Reserved DRSel1 DRSel0 NVEnable
X9252
