CAT5251

Doc. No. MD-2017 Rev. F

8

© Catalyst Semiconductor, Inc.

Characteristics subject to change without notice

WIPER CONTROL AND DATA REGISTERS

Wiper Control Register (WCR)

The CAT5251 contains four 8-bit Wiper Control

Registers, one for each potentiometer. The Wiper

Control Register output is 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 by the host via Write Wiper Control Register

instruction; it may be written by transferring the

contents of one of four associated Data Registers via

the XFR Data Register instruction; it can be modified

one step at a time by the Increment/decrement

instruction (see Instruction section for more details).

Finally, it is loaded with the content of its data register

zero (DR0) upon power-up.

The Wiper Control Register is a volatile register that

loses its contents when the CAT5251 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.

Data Registers (DR)

Each potentiometer has four 8-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 associated Wiper Control

Register. Any data changes in one of the Data

Registers is a non-volatile operation and will take a

maximum of 5ms.

If the application does not require storage of multiple

settings for the potentiometer; the Data Registers can

be used as standard memory locations for system

parameters or user preference data.

Write in Process

The contents of the Data Registers are saved to

nonvolatile memory when the CS

¯¯¯ input goes HIGH

after a write sequence is received. The status of the

internal write cycle can be monitored by issuing a

Read Status command to read the Write in Process

(WIP) bit.

INSTRUCTIONS

Four of the ten instructions are three bytes in length.

These instructions are:

— Read Wiper Control Register – read the current

wiper position of the selected potentiometer in

the WCR

— Write Wiper Control Register – change current

wiper position in the WCR of the selected

potentiometer

— Read Data Register – read the contents of the

selected Data Register

— Write Data Register – write a new value to the

selected Data Register

— Read Status – Read the status of the WIP bit which

when set to "1" signifies a write cycle is in progress.

Table 3. Instruction Set

Instruction Set

Operations

Instruction

I3

I2

I1

I0

R1

R0

WCR1/

P1

WCR0/

P0

Read Wiper Control

Register

1

0

0

1

0

0

1/0

1/0

Read the contents of the Wiper Control Register

pointed to by P1-P0

Write Wiper Control

Register

1

0

1

0

0

0

1/0

1/0

Write new value to the Wiper Control Register pointed

to by P1-P0

Read Data Register

1

0

1

1 1/0 1/0

1/0

1/0

Read the contents of the Data Register pointed to by

P1-P0 and R1-R0

Write Data Register

1

1

0

0 1/0 1/0

1/0

1/0

Write new value to the Data Register pointed to by

P1-P0 and R1-R0

XFR Data Register to

Wiper Control Register

1

1

0

1 1/0 1/0

1/0

1/0

Transfer the contents of the Data Register pointed to

by P1-P0 and R1-R0 to its associated Wiper Control

Register

XFR Wiper Control

Register to Data Register

1

1

1

0 1/0 1/0

1/0

1/0

Transfer the contents of the Wiper Control Register

pointed to by P1-P0 to the Data Register pointed to by

R1-R0

Global XFR Data Registers

to Wiper Control Registers

0

0

0

1 1/0 1/0

0

0

Transfer the contents of the Data Registers pointed to by

R1-R0 of all four pots to their respective Wiper Control

Registers

Global XFR Wiper Control

Registers to Data Register

1

0

0

0 1/0 1/0

0

0

Transfer the contents of both Wiper Control Registers

to their respective data Registers pointed to by R1-R0

of all four pots

Increment/Decrement

Wiper Control Register

0

0

1

0

0

0

1/0

1/0

Enable Increment/decrement of the Control Latch

pointed to by P1-P0

Read Status (WIP bit)

0

1

0

1

0

0

0

1

Read WIP bit to check internal write cycle status

Note: 1/0 = data is one or zero