7
FN8209.2
August 31, 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 X9523 might
experience in a Hot Pluggable situation. On power-up,
V1 / Vcc applied to the X9523 may exhibit some amount
of ringing, before it settles to the required value.
The device is designed such that the wiper terminal
(R
Wx
) is recalled to the correct position (as per the last
stored in the DCP NVM), when the voltage applied to
V1/Vcc exceeds V
TRIP1
for a time exceeding t
purst
(the
Power-on Reset time, set in the CONSTAT Register -
See “CONTROL AND STATUS REGISTER” on
page 10.).
Therefore, if
t
trans
is defined as the time taken for V1 /
Vcc to settle above V
TRIP1
(Figure 7): then the desired
wiper terminal position is recalled by (a maximum) time:
t
trans
+ t
purst
. It should be noted that t
trans
is determined
by system hot plug conditions.
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 V1/Vcc of
the X9523 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 V1/Vcc 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 determine 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 Address is 0), the Most Significant Bit of
the Instruction Byte (I7), determines the Write Type (WT)
performed.
If WT is “1”, then a Nonvolatile Write to the DCP
occurs.
In this case, the “wiper position” of the DCP is changed
by simultaneously writing new data to the associated
Figure 7. DCP Power-up
t
V1/Vcc
V
TRIP1
V1/Vcc (Max.)
t
purst
Maximum Wiper Recall time
0
t
trans
X9523
