X9271 Datasheet, PDF (8/22 Pages) Xicor Inc. – Single Digitally-Controlled (XDCP) Potentiometer

Table 5. Instruction Byte Format
Instruction Opcode
I3
I2
(MSB)
I1
P0
X9271
Register Selection
RB
RA
P1 and P0 are used also for register Bank Selection
for SPI Register Write and Read operations
Pot Selection (WCR Selection)
Set to P0=0 for potentiometer operations
P1
P0
(LSB)
DEVICE DESCRIPTION
Instructions
Five of the eight instructions are three bytes in length.
These instructions are:
– Read Wiper Counter Register – read the current
wiper position of the potentiometer;
– Write Wiper Counter Register – change current
wiper position of the 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 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 will be 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 potentiometers and one of its
associated registers; 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 4).
Two instructions require a two-byte sequence to
complete (Figure 2). These instructions transfer data
between the host and the X9271; 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.
The final command is Increment/Decrement (Figure 5
and 6). It is different from the other commands,
because it’s length is indeterminate. Once the
command is issued, the master can clock the selected
wiper up and/or down in one resistor 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 will move one resistor segment
towards the R_H terminal. Similarly, for each SCK clock
pulse while SI is LOW, the selected wiper will move
one resistor segment towards the R_L terminal.
See Instruction format for more details.
Write in Process (WIP bit)
The contents of the Data Registers are saved to
nonvolatile memory when the CS pin goes from LOW
to HIGH after a complete write sequence is received
by the device. The progress of this internal write
operation can be monitored by a Write In Process bit
(WIP). The WIP bit is read with a Read Status
command.
8
FN8174.1
March 31, 2005