wms7202 Winbond Electronics Corp America, wms7202 Datasheet - Page 7

• Manufacturer Part Number: wms7202
• Description: 256-tap Dual-channel Non-volatile Digital
• Manufacturer: Winbond Electronics Corp America

7. FUNCTIONAL DESCRIPTION
The WMS7202 series, a family of 256-tap, nonvolatile digitally programmable potentiometers is
designed to operate as both a potentiometer or a variable resistor depending upon the output
configuration selected.
The chip can store four 9-bit words in nonvolatile memory (NVMEM0 ~ NVMEM3) and the word stored
in the NVMEM0 will be used to set the tap register values when the device is powered up.
The WMS7202 is controlled by a serial SPI interface that allows setting tap register values as well as
storing data in the nonvolatile memory.
The WMS7202 can operate as either a rheostat or as a potentiometer (voltage divider). When in the
potentiometer configuration there are two possible modes. One is without the output buffer and the
other mode is with the output buffer. Selecting the mode is done by controlling bit D8 of the data
register. D8 = 0 sets the output buffer off and D8 = 1 sets it on. Each channel can be independently
set to either buffer On or Off.
Note that this bit can only be set by loading the value to the NVMEM with instructions #5 and
then loading the TAP register with instruction #6 from NVMEM. This bit cannot be controlled by
directly writing the value to the chip when the tap register is set.
The WMS7202 acts as a two terminal resistive element in the rheostat configuration where one
terminal is either one of the end point pins of the resistor (VA and VB) and the other terminal is the
wiper (VW) pin. This configuration controls the resistance between the two terminals and the
resistance can be adjusted by sending the corresponding tap register setting commands to the
WMS7202 or loading a pre-set tap register value from nonvolatile memory NVMEM0 ~ MVMEM3.
In potentiometer configuration an input voltage is connected to one of the end point pins (VA or VB).
The voltage on the wiper pin will be proportional to the voltage difference between VA and VB and the
wiper setting. The resistance cannot be directly measured in this configuration.
Two program modes are available for the WMS7202:
7.1. P
7.2. P
x
x
7.1.1. Rheostat Configuration
7.1.2. Potentiometer Configuration
Direct program mode. The tap register setting can be changed either by loading a
predetermined value from an external microcontroller or by using the UP/DOWN commands.
The UP and DOWN commands change the tap register setting incrementally i.e., 1 LSB at a
time. The UP and DOWN commands will not wrap around at the ends of the scale.
NVMEM restore mode. One of the previously stored settings can be loaded into the TR
register from the non-volatile memory. Four 9-bit non-volatile memories, are available for each
channel to store tap register settings. The first register, NVMEM0, stores the favorite or
default tap register setting that will be loaded into the tap register at system power up or
software power on reset operation.
OTENTIOMETER AND
ROGRAMMING
M
ODES
R
HEOSTAT
M
ODES
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Publication Release Date: January 2003
WMS7202
Revision 1.1