X9421 Datasheet, PDF (6/21 Pages) Xicor Inc. – Single Digitally Controlled (XDCP) Potentiometer

X9421
At both ends of the array and between each resistor
segment is a CMOS switch connected to the wiper
(V_W/R_W) output. Within the individual array only one
switch may be turned on at a time.
These switches are controlled by a Wiper Counter
Register (WCR). The six bits of the WCR are decoded to
select, and enable, one of sixty-four switches. The block
diagram of the potentiometer is shown in Figure 1.
Wiper Counter Register (WCR)
The X9421 contains a Wiper Counter Register. The
WCR 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 Wiper Counter Register is a volatile register; that
is, its contents are lost when the X9421 is powered-
down. Although the register is automatically loaded
with the value in DR0 upon power-up, this may be
different from the value present at power-down.
Data Registers
The potentiometer has four 6-bit nonvolatile Data
Registers. These can be read or written directly by the
host. Data can also be transferred between any of the
four Data Registers and the WCR. It should be noted all
operations changing data in one of the Data 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, the Data Registers can
be used as regular memory locations for system
parameters or user preference data.
Register Descriptions
Table 1. Data Registers, (6-bit), Nonvolatile
0 0 D5 D4 D3 D2 D1 D0
(MSB)
(LSB)
There are four 6-bit Data Registers associated with the
potentiometer.
– {D5~D0}: These bits are for general purpose Non-
volatile data storage or for storage of up to four dif-
ferent wiper values.
Table 2. Wiper Counter Register, (6-bit), Volatile
0 0 WP5 WP4 WP3 WP2 WP1 WP0
(MSB)
(LSB)
– {WP5~WP0}: These bits specify the wiper position
of the potentiometer.
6
FN8196.1
September 23, 2005