Microchip Technology TSSOP20EV Data Sheet

DS22233A-page 40

© 2009 Microchip Technology Inc.

Each tap point (between the R

S

 resistors) is a

connection point for an analog switch. The opposite
side of the analog switch is connected to a common
signal which is connected to the Terminal W (Wiper)
pin. 

A value in the volatile wiper register selects which
analog switch to close, connecting the W terminal to
the selected node of the resistor ladder.

The wiper can connect directly to Terminal B or to
Terminal A. A zero scale connections, connects the
Terminal W (wiper) to Terminal B (wiper setting of
000h). A full scale connections, connects the Terminal
W (wiper) to Terminal A (wiper setting of 100h or 80h).
In these configurations the only resistance between the
Terminal W and the other Terminal (A or B) is that of the
analog switches.

A wiper setting value greater than full scale (wiper
setting of 100h for 8-bit device or 80h for 7-bit devices)
will also be a Full Scale setting (Terminal W (wiper)
connected to Terminal A). 

 illustrates the full

wiper setting map.

 illustrates the calculation used to

determine the resistance between the wiper and
terminal B.

The MCP43XX device’s WiperLock technology allows
application-specific calibration settings to be secured in
the EEPROM without requiring the use of an additional
write-protect pin. There are four WiperLock Technology
configuration bits (WL0, WL1, WL2, and WL3). These
bits prevent the Non-Volatile and Volatile addresses
and bits for the specified resistor network from being
written. 

The WiperLock technology prevents the serial
commands from doing the following:

• Changing a volatile wiper value
• Writing to the specified non-volatile wiper memory 

location

• Changing the related volatile TCON register bits

For either Resistor Network 0, Resistor Network 1,
Resistor Network 2, or Resistor Network 3 (Potx), the
WLx bit controls the following:

• Non-Volatile Wiper Register
• Volatile Wiper Register
• Volatile TCON register bits RxHW, RxA, RxW, and 

RxB

High Voltage commands are required to enable and
disable WiperLock. Please refer to the 

command for operation.

5.3.1

POR/BOR OPERATION WHEN 
WIPERLOCK TECHNOLOGY 
ENABLED 

The WiperLock Technology state is not affected by a
POR/BOR event. A POR/BOR event will load the
Volatile Wiper register value with the Non-Volatile
Wiper register value, refer to Section 4.1.

3FFh –

081h

3FFh –

101h

Reserved (Full Scale (W = A)),
Increment and Decrement 
commands ignored 

080h

100h

Full Scale (W = A), 
Increment commands ignored 

07Fh –

041h

0FFh –

081h

W = N

040h

080h

W = N (Mid Scale)

03Fh –

001h

07Fh –

001h

W = N

000h

000h

Zero Scale (W = B)
Decrement command ignored

(

)

N = 0 to 256 (decimal)

(

)

N = 0 to 128 (decimal)

8-bit Device

7-bit Device