CAT5259

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9

Figure 9. Instruction Byte Format

I3

I2

I1

I0

R1

R0

P1

P0

(MSB)

(LSB)

Instruction

Data Register

WCR/Pot Selection

Opcode

Selection

WIPER CONTROL AND DATA REGISTERS

Wiper Control Register (WCR)

The CAT5259 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 CAT5259 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 10 ms.

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.

Instructions

Four of the nine instructions are three bytes in length.

These instructions are:

position of the selected potentiometer in the WCR

position in the WCR of the selected potentiometer

Data Register

selected Data Register

Instruction

Instruction Set

Operation

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

Gang 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

Gang 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