8
FN8208.2
September 7, 2010
The data in the WCR is then decoded to select and
enable one of the respective FET switches. A
“make before break” sequence is used internally
for the FET switches when the wiper is moved
from one tap position to another.
Hot Pluggability
Figure 7 shows a typical waveform that the X9522
might experience in a Hot Pluggable situation. On
power-up, Vcc / V1 applied to the X9522 may
exhibit some amount of ringing, before it settles to
the required value.
The device is designed such that the wiper termi-
nal (R
Wx
) is recalled to the correct position (as per
the last stored in the DCP NVM), when the voltage
applied to Vcc / V1 exceeds V
TRIP
for a time
exceeding t
pu.
Therefore, if t
trans
is defined as the time taken for
Vcc / V1 to settle above V
TRIP
(Figure 7): then the
desired wiper terminal position is recalled by (a
maximum) time:
t
trans
+ t
pu
. It should be noted
that
t
trans
is determined by system hot plug con-
ditions.
DCP Operations
In total there are three operations that can be
performed on any internal DCP structure:
—DCP Nonvolatile Write
—DCP Volatile Write
—DCP Read
A nonvolatile write to a DCP will change the “wiper
position” by simultaneously writing new data to
the associated WCR and NVM. Therefore, the new
“wiper position” setting is recalled into the WCR
after Vcc / V1 of the X9522 is powered down and
then powered back up.
A volatile write operation to a DCP however,
changes the “wiper position” by writing new data
to the associated WCR only. The contents of the
associated NVM register remains unchanged.
Therefore, when Vcc / V1 to the device is powered
down then back up, the “wiper position” reverts to
that last position written to the DCP using a
nonvolatile write operation.
Both volatile and nonvolatile write operations are
executed using a three byte command sequence:
(DCP) Slave Address Byte, Instruction Byte,
followed by a Data Byte (See Figure 9).
A DCP Read operation allows the user to “read
out” the current “wiper position” of the DCP, as
stored in the associated WCR. This operation is
executed using the Random Address Read
command sequence, consisting of the (DCP) Slave
Address Byte followed by an Instruction Byte and
the Slave Address Byte again (Refer to Figure 10.).
Instruction Byte
While the Slave Address Byte is used to select the
DCP devices, an Instruction Byte is used to deter-
mine which DCP is being addressed.
The Instruction Byte (Figure 8) is valid only when
the Device Type Identifier and the Internal Device
Address bits of the Slave Address are set to
1010111. In this case, the two Least Significant
Bit’s (I1 - I0) of the Instruction Byte are used to
select the particular DCP (0 - 2). In the case of a
Write to any of the DCPs (i.e. the LSB of the Slave
Figure 7. DCP Power-up
t
Vcc
V
TRIP
Vcc (Max.)
t
pu
Maximum Wiper Recall time
0
t
trans
X9522
