X9251
7
FN8166.6
December 3, 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
• Read Status – this command returns the contents of the WIP
bit which indicates if the internal write cycle is in progress
The basic sequence of the three-byte instructions is illustrated in
Figure 4
. 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. The Read Status Register instruction
is the only unique format (see Figure 6
).
Four instructions require a two-byte sequence to complete. These
instructions transfer data between the host and the X9251;
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 (see Figures 7 and 8).
The Increment/Decrement command is different from the other
commands. Once the command is issued and the X9251 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 SCK clock
pulse (t
HIGH
) while SI is HIGH, the selected wiper moves one
wiper position towards the R
H
terminal. Similarly, for each SCK
clock pulse while SI is LOW, the selected wiper moves one wiper
position towards the R
L
terminal. A detailed illustration of the
sequence and timing for this operation are shown. See
“
Instruction Format” on page 10 for more details.
XFR Wiper Counter
Register to Data Register
1 1 1 0 1/0 1/0 1/0 1/0 Transfer the contents of the Wiper Counter Register
pointed to by P1, P0 to the Data Register pointed to
by RB, RA
Global XFR Data Registers to Wiper
Counter Registers
0 0 0 1 1/0 1/0 0 0 Transfer the contents of the Data Registers pointed to
by RB, RA of all four pots to their respective Wiper
Counter Registers
Global XFR Wiper Counter Registers
to Data Register
1 0 0 0 1/0 1/0 0 0 Transfer the contents of both Wiper Counter Registers
to their respective data Registers pointed to by RB, RA
of all four pots
Increment/Decrement
Wiper Counter Register
0 0 1 0 0 0 1/0 1/0 Enable Increment/decrement of the Control Latch
pointed to by P1, P0
NOTE: 1/0 = data is one or zero
TABLE 5. INSTRUCTION SET (Continued)
INSTRUCTION
INSTRUCTION SET
OPERATIONI3 I2 I1 I0 RB RA P1 P0
