6

FN8174.1

March 31, 2005

DEVICE DESCRIPTION

Wiper Counter Register (WCR)

The X9271 contains a Wiper Counter Register for the

DCP potentiometer. The Wiper Counter Register can

be envisioned as a 8-bit parallel and serial load

counter with its outputs decoded to select one of 256

switches along its resistor array. The contents of the

WCR can be altered in four ways: it may be written

directly by the host via the Write Wiper Counter

Register instruction (serial load); it may be written

indirectly by transferring the contents of one of four

associated data registers via the XFR Data Register

instruction (parallel load); it can be modified one step

at a time by the Increment/ Decrement instruction.

Finally, it is loaded with the contents of its Data

Register zero (DR0) upon power-up.

The Wiper Counter Register is a volatile register; that

is, its contents are lost when the X9271 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 R0 value into the WCR. The

DR0 value of Bank 0 is the default value.

Data Registers (DR3–DR0)

The potentiometer has four 8-bit nonvolatile 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 associated 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.

Bits [7:0] are used to store one of the 256 wiper

positions or data (0 ~255).

Status Register (SR)

This 1-bit Status Register is used to store the system

status.

WIP: Write In Progress status bit, read only.

– When WIP=1, indicates that high-voltage write cycle

is in progress.

– When WIP=0, indicates that no high-voltage write

cycle is in progress

Table 1. Wiper counter Register, WCR (8-bit), WCR[7:0]: Used to store the current wiper position (Volatile, V).

Table 2. Data Register, DR (8-bit), DR[7:0]: Used to store wiper positions or data (Nonvolatile, NV).

Table 3. Status Register, SR (WIP is 1-bit)

WCR7

WCR6

WCR5

WCR4

WCR3

WCR2

WCR1

WCR0

VVVVVVVV

(MSB)

(LSB)

Bit 7Bit 6Bit 5Bit 4Bit 3Bit 2Bit 1Bit 0

NV

NV

NV

NV

NV

NV

NV

NV

MSB

LSB

WIP

(LSB)

X9271