X9521 datasheet(8/24 Pages) RENESAS

8 / 24 page

X9521

FN8207 Rev 2.00

Page 8 of 24

September 21, 2010

number of bits. Also, setting the bits (P1 = 0, P0 = 0) or (P1

= 1, P0 = 1) are reserved sequences, and will result in no

ACKNOWLEDGE after sending an Instruction Byte on

SDA.

The factory default setting of all “wiper position” settings is

with 00h stored in the NVM of the DCPs. This corresponds

to having the “wiper teminal” RWX (x=1,2) at the “lowest”

tap position, Therefore, the resistance between RWX and

RLX is a minimum (essentially only the Wiper Resistance,

RW).

DCP Read Operation

A read of DCPx (x = 1,2) can be performed using the three

byte random read command sequence shown in Figure 11.

The master issues the START condition and the Slave

Address Byte 10101110 which specifies that a “dummy”

write” is to be conducted. This “dummy” write operation

sets which DCP is to be read (in the preceding Read oper-

ation). An ACKNOWLEDGE is returned by the X9521 after

the Slave Address if received correctly. Next, an Instruction

Byte is issued on SDA. Bits P1 - P0 of the Instruction Byte

determine which DCP “wiper position” is to be read. In this

case, the state of the WT bit is “don’t care”. If the Instruction

Byte format is valid, then another ACKNOWLEDGE is

returned by the X9521.

Following this ACKNOWLEDGE, the master immediately

issues another START condition and a valid Slave address

byte with the R/W bit set to 1. Then the X9521 issues an

ACKNOWLEDGE followed by Data Byte, and finally, the

master issues a STOP condition. The Data Byte read in

this operation, corresponds to the “wiper position” (value of

the WCR) of the DCP pointed to by bits P1 and P0.

It should be noted that when reading out the data byte for

DCP1 (100 Tap), the upper most significant bit is an

“unknown”. For DCP2 (256 Tap) however, all bits of the

data byte are relevant (See Figure 11).

Slave

Address

Byte

Data

(n)

SDA Bus

Signals from

the Slave

Signals from

the Master

Data

(1)

(2 < n < 16)

Figure 10. EEPROM Page Write Operation

1 01 0 0 0 0 0

Slave

Address

Instruction

Byte

Slave

Address

Data Byte

SDA Bus

Signals from

the Slave

Signals from

the Master

Figure 11. DCP Read Sequence

“Dummy” write

READ Operation

10 1 1 11 0

00 00

10 1 1 11 1

WRITE Operation

MSB

LSB

DCPx

x = 1

x = 2

“-” = DON’T CARE

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