10
FN8197.1
April 26, 2006
DETAILED OPERATION
The potentiometer has a Wiper Counter Register and
four Data Registers. A detailed discussion of the
register organization and array operation follows.
Wiper Counter Register
The X9428 contains a Wiper Counter Register. The
Wiper Counter Register can be envisioned as a 6-bit
parallel and serial load counter with its outputs
decoded to select one of sixty-four switches along its
resistor array. The contents of the WCR can be altered
in four ways: it may be written directly by the host via
the write Wiper Counter Register instruction (serial
load); it may be written indirectly by transferring the
contents of one of four associated Data Registers via
the XFR Data Register instruction (parallel load); it can
be modified one step at a time by the
Increment/Decrement instruction. Finally, it is loaded
with the contents of its Data Register zero (DR0) upon
power-up.
The WCR is a volatile register; that is, its contents are
lost when the X9428 is powered-down. Although the
register is automatically loaded with the value in DR0
upon power-up, it should be noted this may be
different from the value present at power-down.
Data Registers
The potentiometer has four nonvolatile Data
Registers. These can be read or written directly by the
host and data can be transferred between any of the
four Data Registers and the Wiper Counter Register. It
should be noted all operations changing data in one of
these registers is a nonvolatile operation and will take
a maximum of 10ms.
If the application does not require storage of multiple
settings for the potentiometer, these registers can be
used as regular memory locations that could possibly
store system parameters or user preference data.
Register Descriptions
Data Registers, (6-Bit), Nonvolatile
Four 6-bit Data Registers for each XDCP. (eight 6-bit
registers in total).
– {D5~D0}: These bits are for general purpose not
volatile data storage or for storage of up to four
different wiper values. The contents of Data Register
0 are automatically moved to the Wiper Counter
Register on power-up.
Wiper Counter Register, (6-Bit), Volatile
One 6-bit wiper counter register for each XDCP. (Four
6-bit registers in total.)
– {D5~D0}: These bits specify the wiper position of the
respective XDCP. The Wiper Counter Register is
loaded on power-up by the value in Data Register 0.
The contents of the WCR can be loaded from any of
the other Data Register or directly. The contents of
the WCR can be saved in a DR.
D5 D4 D3 D2 D1 D0
NV NV NV NV NV NV
(MSB) (LSB)
WP5 WP4 WP3 WP2 WP1 WP0
VVVVVV
(MSB) (LSB)
X9428
