MCP414X/416X/424X/426X
5.2
Wiper
5.3
WiperLock™ Technology
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 deter-
mine the resistance between the wiper and terminal B.
The MCP4XXX 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 two WiperLock Technology
configuration bits (WL0 and WL1). These bits prevent
the Non-Volatile and Volatile addresses and bits for the
specified resistor network from being written.
The WiperLock technology prevents
commands from doing the following:
the
serial
• Changing a volatile wiper value
• Writing to a non-volatile wiper memory location
• Changing the volatile TCON register value
For either Resistor Network 0 or Resistor Network 1
(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
EQUATION 5-2:
R
WB
CALCULATION
8-bit Device
R
AB
N
R
WB
= ------------- + R
W
-
(
256
)
N = 0 to 256 (decimal)
R
AB
N
-
R
WB
= ------------- + R
W
(
128
)
N = 0 to 128 (decimal)
7-bit Device
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
TABLE 5-1:
VOLATILE WIPER VALUE VS.
WIPER POSITION MAP
Properties
Wiper Setting
7-bit Pot 8-bit Pot
3FFh
081h
080h
07Fh
041h
040h
03Fh
001h
000h
3FFh
101h
100h
0FFh
081
080h
07Fh
001
000h
Reserved (Full Scale (W = A)),
Increment and Decrement
commands ignored
Full Scale (W = A),
Increment commands ignored
W=N
W = N (Mid-Scale)
W=N
Zero Scale (W = B)
Decrement command ignored
DS22059B-page 36
©
2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP TECHNOLOGY ]
