8
FN8199.0
March 11, 2005
REGISTER OPERATION
Both digitally controlled potentiometers share the
serial interface and share a common architecture.
Each potentiometer is associated with a Wiper
Counter Register (WCR), and four Data Registers.
Figure 7 illustrates the control, registers, and system
features of the device.
Figure 7. System Block Diagram
Wiper Counter (WCR) and Analog Control Registers
(ACR)
The X9438 contains two wiper counter registers, one
for each XDCP. The wiper counter register is equiva-
lent to a serial-in, parallel-out counter, with its outputs
decoded to select one of sixty-four switches along its
resistor array. The contents of the wiper counter regis-
ter can be altered in four ways: it may be written
directly by the host via the write WCR Instruction
(serial load); it may be written indirectly by transferring
the contents of one of four associated data registers
(DR) via the XFR data register instruction (parallel
load); it can be modified one step at a time by the
increment/decrement instruction (WCR only). Finally,
it is loaded with the contents of its data register zero
(R0) upon power-up.
The wiper counter register is a volatile register; that is,
its contents are lost when the X9438 is powered-down.
Although the registers are automatically loaded with the
value in R0 upon power-up, it should be noted this may
be different from the value present at power-down.
Data Registers (DR)
Each potentiometer has four non-volatile data registers
(DR). These can be read or written directly by the host
and data can be transferred between any of the four
data registers and the WCR. It should be noted all oper-
ations changing data in one of these registers is a non-
volatile 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 store sys-
tem parameters or user preference data.
REGISTER DESCRIPTIONS AND MEMORY MAP
Memory Map
Wiper Counter Register (WCR)
WP0-WP5 identify wiper position.
Data Registers (DR, R0 - R3)
V
OUT (0,1)
(DR0-DR3)
0,1
Interface
and
Control
Circuitry
SCL
SDA
A0
A1
A2
A3
V
H (0,1)
V
L (0,1)
WP
V
W (0,1)
V
NI (0,1)
+
–
WCR
0,1
V
INV (0,1)
WCRO WCR1
DR0 DR0
DR1 DR1
DR2 DR2
DR3 DR3
0 0 WP5 WP4 WP3 WP2 WP1 WP0
(volatile) (LSB)
Wiper Position or User Data
(Nonvolatile)
X9438
