7

FN8161.4

December 4, 2009

Instruction and Register Description

DEVICE ADDRESSING

Wiper Counter Register (WCR)

The X9118 contains a Wiper Counter Register (see Table 4)

for the XDCP potentiometer. The WCR is equivalent to a

serial-in, parallel-out register/counter with its outputs

decoded to select one of 1024 switches along its resistor

array. The contents of the WCR can be altered in one of

three ways:

1. It may be written directly by the host via the write Wiper

Counter Register instruction (serial load)

2. It may be written indirectly by transferring the contents of

one of four associated Data Registers via the XFR Data

register

3. It is loaded with the contents of its Data Register zero

(R0) upon power-up.

The Wiper Counter Register is a volatile register; that is, its

contents are lost when the X9118 is powered-down. Although

the register is automatically loaded with the value in DR0

upon power-up, this may be different from the value present at

power-down. Power-up guidelines are recommended to

ensure proper loadings of the DR0 value into the WCR.

Data Registers (DR)

The potentiometer has four 10-bit non-volatile Data

Registers. These can be read or written directly by the host.

Data can also be transferred between any of the four data

registers and the Wiper Counter Register. All operations

changing data in one of the Data Registers is a nonvolatile

operation and will take a maximum of 10ms.

If the application does not require storage of multiple

settings for the potentiometer, the Data Registers can be

used as regular memory locations for system parameters or

user preference data.

Bit 9–Bit 0 are used to store one of the 1024 wiper position

(0 ~1023).

Four of the six instructions are four bytes in length. These

instructions are:

• Read Wiper Counter Register – read the current wiper

position of the potentiometer,

• Write Wiper Counter Register – change current wiper

position of the potentiometer,

• Read Data Register – read the contents of the selected

Data Register;

• Write Data Register – write a new value to the selected

Data Register.

The basic sequence of the four byte instructions is illustrated

in Figure 3. These four-byte instructions exchange data

between the WCR and one of the Data Registers. A transfer

from a data register to a WCR is essentially a write to a static

RAM, with the static RAM controlling the wiper position. The

transfer from the WCR (current wiper position), to a data

register is a write to nonvolatile memory and takes a minimum

potentiometer and one of its associated registers.

Two instructions (see Figure 4) require a two-byte sequence

to complete. These instructions transfer data between the

host and the X9118; either between the host and one of the

Data Registers or directly between the host and the Wiper

Counter Register. These instructions are:

• XFR Data Register to Wiper Counter Register – This

transfers the contents of one specified Data Register to

the Wiper Counter Register.

• XFR Wiper Counter Register to Data Register –This

transfers the contents of the specified Wiper Counter

Register to the specified Data Register.

See “Instruction Format” on page 8 for more details.

Other

POWER-UP AND DOWN REQUIREMENTS

At all times, the V+ voltage must be greater than or equal to

greater than or equal to the voltage at V-. During power-up

values within 1ms of each other.

TABLE 4. WIPER CONTROL REGISTER, WCR (10-BIT), WCR9–WCR0: USED TO STORE THE CURRENT WIPER POSITION (VOLATILE, V)

WCR9

WCR8

WCR7

WCR6

WCR5

WCR4

WCR3

WCR2

WCR1

WCR0

VVV

VVVVVVV

(MSB)

(LSB)

TABLE 5. DATA REGISTER, DR (10-BIT), BIT 9–BIT 0: USED TO STORE WIPER POSITIONS OR DATA (NON-VOLATILE, NV)

BIT 9

BIT 8

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

NV

NV

NV

NV

NV

NV

NV

NV

NV

NV

MSB

LSB

X9118