X9251-2.7 INTERSIL [Intersil Corporation], X9251-2.7 Datasheet - Page 8

• Manufacturer Part Number: X9251-2.7
• Description: Single Supply/Low Power/256-Tap/SPI Bus
• Manufacturer: INTERSIL [Intersil Corporation]

Instructions
Four of the nine instructions are three bytes in length.
These instructions are:
– Read Wiper Counter Register – read the current
– Write Wiper Counter Register – change current
– Read Data Register – read the contents of the
– Write Data Register – write a new value to the
– Read Status – this command returns the contents
The basic sequence of the three byte instructions is
illustrated in Figure 3. 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
the WCR (current wiper position), to a Data Register is
a write to non-volatile memory and takes a minimum of
t
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 5).
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:
WR
wiper position of the selected potentiometer,
wiper position of the selected potentiometer,
selected Data Register,
selected Data Register,
of the WIP bit which indicates if the internal write
cycle is in progress.
to complete. The transfer can occur between one
8
WRL
. A transfer from
X9251
– XFR Data Register to Wiper Counter Register –
– XFR Wiper Counter Register to Data Register –
– Global XFR Data Register to Wiper Counter
– Global XFR Wiper Counter Register to Data
INCREMENT/DECREMENT COMMAND
The final command is Increment/Decrement (See
Figures 6 and 7). 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
the selected wiper moves one wiper position towards
the R
while SI is LOW, the selected wiper moves one wiper
position towards the R
of the sequence and timing for this operation are
shown. See Instruction format for more details.
This transfers the contents of one specified Data
Register to the associated Wiper Counter Register.
This transfers the contents of the specified Wiper
Counter Register to the specified associated Data
Register.
Register – This transfers the contents of all speci-
fied Data Registers to the associated Wiper Counter
Registers.
Register – This transfers the contents of all Wiper
Counter Registers to the specified associated Data
Registers.
H
terminal. Similarly, for each SCK clock pulse
L
terminal. A detailed illustration
HIGH
) while SI is HIGH,
September 14, 2005
FN8166.2