X9259
8
FN8169.6
December 12, 2014
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Instructions
Four of the nine instructions are three bytes in length. These
instructions are:
• Read Wiper Counter Register – read the current wiper position
of the selected potentiometer.
• Write Wiper Counter Register – change current wiper position
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.
The basic sequence of the three byte instructions is illustrated in
Figure 5
. These three-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 to this action is delayed by t
WRL
. A transfer from the WCR
(current wiper position), to a Data Register is a write to
nonvolatile memory and takes a minimum of t
WR
to complete.
The transfer can occur between one of the four potentiometer’s
WCR, and one of its associated registers, DRs; or it may occur
globally, where the transfer occurs between all potentiometers
and one associated register.
Four instructions require a two-byte sequence to complete. These
instructions transfer data between the host and the X9259;
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 associated
Wiper Counter Register.
• XFR Wiper Counter Register to Data Register – This transfers
the contents of the specified Wiper Counter Register to the
specified associated Data Register.
• Global XFR Data Register to Wiper Counter
Register – This transfers the contents of all specified Data
Registers to the associated Wiper Counter Registers.
• Global XFR Wiper Counter Register to Data
Register – This transfers the contents of all Wiper Counter
Registers to the specified associated Data Registers.
Increment/Decrement Command
The final command is Increment/Decrement (Figures 6 and 7).
The Increment/Decrement command is different from the other
commands. Once the command is issued and the X9259 has
responded with an Acknowledge, the master can clock the
selected wiper up and/or down in one segment steps; thereby,
providing a fine tuning capability to the host. For each SCL clock
pulse (t
HIGH
) while SDA is HIGH, the selected wiper moves one
wiper position towards the R
H
terminal. Similarly, for each SCL
clock pulse while SDA is LOW, the selected wiper moves one
resistor wiper position towards the R
L
terminal.
See “
Instruction Format” on page 10 for more details.
FIGURE 4. TWO-BYTE INSTRUCTION SEQUENCE
FIGURE 5. THREE-BYTE INSTRUCTION SEQUENCE 2-WIRE INTERFACE
S
T
A
R
T
0101
A2 A0
A
C
K
I2 I1
I0
RB RA P1
A
C
K
SCL
SDA
S
T
O
P
ID3 ID2 ID1 ID0
P0
Device ID
External
Instruction
Opcode
Address
Register
Address
DCP/WCR
Address
A1
A3
I3
I3
I2
I1
I0
RB RA
ID3 ID2
ID1
ID0
Device ID
External
Instruction
Opcode
Address
Register
Address
Pot/WCR
Address
Data for WCR[7:0] or DR[7:0]
S
T
A
R
T
0 101
A2 A1 A0
A
C
K
P1 P0 A
C
K
SCL
SDA
S
T
O
P
A
C
K
D7 D6 D5 D4 D3 D2 D1 D0
A3
