X9521 datasheet(7/24 Pages) RENESAS

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X9521

FN8207 Rev 2.00

Page 7 of 24

September 21, 2010

If WT is “0” then a DCP Volatile Write is performed. This

operation changes the DCP “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 written to the DCP using

a nonvolatile write operation.

DCP Write Operation

A write to DCPx (x = 1,2) can be performed using the three

byte command sequence shown in Figure 9.

In order to perform a write operation on a particular DCP,

the Write Enable Latch (WEL) bit of the CONSTAT Regis-

ter must first be set (See “BL1, BL0: Block Lock protection

bits - (Nonvolatile)” on page 12.)

The Slave Address Byte 10101110 specifies that a Write to

a DCP is to be conducted. An ACKNOWLEDGE is

returned by the X9521 after the Slave Address, if it has

been received correctly.

Next, an Instruction Byte is issued on SDA. Bits P1 and P0

of the Instruction Byte determine which WCR is to be writ-

ten, while the WT bit determines if the Write is to be volatile

or nonvolatile. If the Instruction Byte format is valid, another

ACKNOWLEDGE is then returned by the X9521.

Following the Instruction Byte, a Data Byte is issued to the

X9521 over SDA. The Data Byte contents is latched into

the WCR of the DCP on the first rising edge of the clock

signal, after the LSB of the Data Byte (D0) has been issued

on SDA (See Figure 25).

The Data Byte determines the “wiper position” (which FET

switch of the DCP resistive array is switched ON) of the

DCP. The maximum value for the Data Byte depends upon

which DCP is being addressed (see Table below).

Using a Data Byte larger than the values specified above

results in the “wiper terminal” being set to the highest tap

position. The “wiper position” does NOT roll-over to the

lowest tap position.

For DCP2 (256 Tap), the Data Byte maps one to one to the

“wiper position” of the DCP “wiper terminal”. Therefore, the

Data Byte 00001111 (1510) corresponds to setting the

“wiper terminal” to tap position 15. Similarly, the Data Byte

00011100 (2810) corresponds to setting the “wiper termi-

nal” to tap position 28. The mapping of the Data Byte to

“wiper position” data for DCP1 (100 Tap), is shown in

“APPENDIX 1” . An example of a simple C language func-

tion which “translates” between the tap position (decimal)

and the Data Byte (binary) for DCP1, is given in “APPEN-

DIX 2” .

It should be noted that all writes to any DCP of the X9521

are random in nature. Therefore, the Data Byte of consecu-

tive write operations to any DCP can differ by an arbitrary

WT†

Description

Select a Volatile Write operation to be performed

on the DCP pointed to by bits P1 and P0

Select a Nonvolatile Write operation to be per-

formed on the DCP pointed to by bits P1 and P0

WRITE TYPE

DCP SELECT

†

This bit has no effect when a Read operation is being performed.

Figure 8.

Instruction Byte Format

101

01110

P1 P0 A

D7 D6 D5 D4 D3 D2 D1 D0

SLAVE ADDRESS BYTE

INSTRUCTION BYTE

DATA BYTE

Figure 9.

DCP Write Command Sequence

P1 - P0

DCPx

# Taps

Max. Data Byte

Reserved

x = 1

100

Refer to Appendix 1

x = 2

256

FFh

Reserved

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