8
FN8194.3
October 12, 2006
Figure 8. Detailed Potentiometer Block Diagram
DETAILED OPERATION
Both XDCP potentiometers share the serial interface
and share a common architecture. Each 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 X9418 contains two wiper counter registers, one
for each XDCP potentiometer. 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 X9418 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
Each 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.
Serial Data Path
From Interface
Circuitry
Register 0 Register 1
Register 2 Register 3
Serial
Bus
Input
Parallel
Bus
Input
Wiper
Counter
Register
INC/DEC
Logic
UP/DN
CLK
Modified SCL
UP/DN
V
H
/R
H
V
L
/R
L
V
W
/R
W
If WCR = 00[H] then V
W
/R
W
= V
L
/R
L
If WCR = 3F[H] then V
W
/R
W
= V
H
/R
H
8 6
C
o
u
n
t
e
r
D
e
c
o
d
e
(WCR)
D5 D4 D3 D2 D1 D0
NV NV NV NV NV NV
(MSB) (LSB)
X9418
