X9521 datasheet(7/25 Pages) INTERSIL

7 / 25 page

FN8207.1

August 25, 2005

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. There-

fore, 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 Reg-

ister must first be set (See “BL1, BL0: Block Lock protec-

tion 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

written, 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”. There-

fore, the Data Byte 00001111 (1510) corresponds to set-

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

Data Byte 00011100 (2810) corresponds to setting the

“wiper terminal” 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 lan-

guage function which “translates” between the tap posi-

tion (decimal) and the Data Byte (binary) for DCP1, is

given in “APPENDIX 2” .

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

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

secutive write operations to any DCP can differ by an

arbitrary number of bits. Also, setting the bits (P1 = 0,

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

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

X9521

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