X9408_14 Datasheet, PDF (8/20 Pages) Intersil Corporation – Quad Digitally Controlled Potentiometers

X9408
SERIAL DATA PATH
FROM INTERFACE
CIRCUITRY
REGISTER 0
8
REGISTER 2
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
SERIAL
BUS
INPUT
C
REGISTER 1
O
U
N
6
PARALLEL
T
BUS
E
INPUT
R
REGISTER 3
WIPER
COUNTER
D
REGISTER
E
(WCR)
C
O
D
E
UP/DN
INC/DEC
LOGIC
UP/DN
MODIFIED SCL
CLK
V_H/R_H
V_L/R_L
FIGURE 8. DETAILED POTENTIOMETER BLOCK DIAGRAM
V_W/R_W
Detailed Operation
All 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 X9408 contains four 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 X9408 is powered-down. Although the register is
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
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 WCR. 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
TABLE 2. DATE REGISTERS, (6-BIT), NONVOLATILE
D5
D4
D3
D2
D1
D0
NV
NV
NV
NV
NV
NV
(MSB)
(LSB)
Four 6-bit Data Registers for each XDCP. (sixteen 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.
8
FN8191.4
January 15, 2009