X9259 Datasheet, PDF (5/21 Pages) Xicor Inc. – Quad Digitally-Controlled (XDCP) Potentiometers

X9259
Principles of Operation
The X9259 is an integrated circuit incorporating four DCPs
and their associated registers and counters, and the serial
interface providing direct communication between a host
and the potentiometers.
DCP Description
Each DCP is implemented with a combination of resistor
elements and CMOS switches. The physical ends of each
DCP are equivalent to the fixed terminals of a mechanical
potentiometer (R_H and R_L pins). The RW pin is an
intermediate node, equivalent to the wiper terminal of a
mechanical potentiometer.
The position of the wiper terminal within the DCP is
controlled by an 8-bit volatile Wiper Counter Register
(WCR).
Power Up and Down Recommendations
There are no restrictions on the power-up or power-down
conditions of V_CC and the voltages applied to the
potentiometer pins provided that V_CC is always more
positive than or equal to V_H, V_L, and V_W, i.e., V_CC ≥ V_H, V_L,
V_W. The V_CC ramp rate specification is always in effect.
Wiper Counter Register (WCR)
The X9259 contains four Wiper Counter Registers, one for
each potentiometer. The Wiper Counter Register can be
envisioned as a 8-bit parallel and serial load counter with its
outputs decoded to select one of 256 wiper positions 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 (see Instruction
section for more details). Finally, it is loaded with the
contents of its data register zero (DR#0) upon power-up.
(See Figure 1.)
The Wiper Counter Register is a volatile register; that is, its
contents are lost when the X9259 is powered-down.
Although the register is automatically loaded with the value
in DR#0 upon power-up, this may be different from the value
present at power-down. Power-up guidelines are
recommended to ensure proper loadings of the DR#0 value
into the WCR# (See Design Considerations Section).
Data Registers (DR)
Each of the four DCPs has four 8-bit non-volatile 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 associated Wiper Counter Register. All
operations changing data in one of the data registers is a
non-volatile operation and takes 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.
Bit [7:0] are used to store one of the 256 wiper positions
(0~255).
TABLE 1. WIPER COUNTER REGISTER, WCR (8-bit), WCR[7:0]: Used to store the current wiper position (Volatile).
WCR7
WCR6
WCR5
WCR4
WCR3
WCR2
WCR1
(MSB)
WCR0
(LSB)
TABLE 2. DATA REGISTER, DR (8-BIT), BIT [7:0]: Used to store wiper positions or data (Non-volatile).
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
(MSB)
Bit 1
Bit 0
(LSB)
5
FN8169.2
September 16, 2005