X9420

FN8195 Rev.1.00

Page 6 of 19

April 26, 2006

Two of the eight instructions are two bytes in length and

end with the transmission of the instruction byte. These

instructions are:

– XFR Data Register to Wiper Counter Register —This

instruction transfers the contents of one specified Data

Register to the Wiper Counter Register.

– XFR Wiper Counter Register to Data Register—This

instruction transfers the contents of the Wiper Counter

Register to the specified associated Data Register.

The basic sequence of the two byte instructions is

illustrated in Figure 4. These two-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 response of the wiper

WCR (current wiper position), to a Data Register is a write

complete. The transfer can occur between the

potentiometer and one of its associated registers.

Five instructions require a three-byte sequence to

complete. These instructions transfer data between the

host and the X9420; either between the host and one of

the Data Registers or directly between the host and the

WCR. These instructions are:

– Read Wiper Counter Register—read the current wiper

position of the pot,

– Write Wiper Counter Register—change current wiper

position of the pot,

– 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—This command returns the contents of

the WIP bit which indicates if the internal write cycle is

in progress.

The sequence of these operations is shown in Figure 5

and Figure 6.

The final command is Increment/Decrement. It is

different from the other commands, because it’s length is

indeterminate. Once the command is issued, the master

can clock the wiper up and/or down in one resistor

segment steps; thereby, providing a fine tuning

while SI is HIGH, the selected wiper will move one

for each SCK clock pulse while SI is LOW, the selected

wiper will move one resistor segment towards the

and timing for this operation are shown in Figure 7 and

Figure 8.

Figure 4. Two-Byte Instruction Sequence

0101

110A0

I3

I2

I1

I0

R1 R0

0

0

SCK

SI

CS