X9521 datasheet(6/24 Pages) RENESAS

6 / 24 page

X9521

FN8207 Rev 2.00

Page 6 of 24

September 21, 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 X9521 might

experience in a Hot Pluggable situation. On power-up, Vcc

applied to the X9521 may exhibit some amount of ringing,

before it settles to the required value.

The device is designed such that the wiper terminal (RWx)

is recalled to the correct position (as per the last stored in

the DCP NVM), when the voltage applied to Vcc exceeds

VTRIP for a time exceeding tpu.

Therefore, if

ttrans is defined as the time taken for Vcc to

settle above VTRIP (Figure 7): then the desired wiper ter-

minal position is recalled by (a maximum) time:

ttrans +

tpu. It should be noted that ttrans 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 Vcc of the

X9521 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 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

11.).

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 WCR

and NVM. Therefore, the new “wiper position” setting is

recalled into the WCR after Vcc of the X9521 has been

powered down then powered back up

Figure 7.

DCP Power-up

Vcc

VTRIP

Vcc (Max.)

tpu

Maximum Wiper Recall time

ttrans

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