MCP413X/415X/423X/425X
A POR/BOR event will load the Volatile Wiper register
value with the default value. Table 5-2 shows the
default values offered. Custom POR/BOR options are
available. Contact the local Microchip Sales Office.
5.2
Wiper
Each tap point (between the RS 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.
TABLE 5-2:
DEFAULT FACTORY
SETTINGS SELECTION
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.
Wiper Code
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.
8-bit
7-bit
-502
-103
-503
-104
5.0 kΩ
Mid-scale
Mid-scale
Mid-scale
Mid-scale
80h
80h
80h
80h
40h
40h
40h
40h
10.0 kΩ
50.0 kΩ
100.0 kΩ
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). Table 5-1 illustrates the full
wiper setting map.
Equation 5-2 illustrates the calculation used to deter-
mine the resistance between the wiper and terminal B.
EQUATION 5-2:
R
CALCULATION
WB
RAB
N
RWB = ------------- + RW
8-bit Device
(256)
N = 0 to 256 (decimal)
RAB
N
7-bit Device
RWB = ------------- + RW
(128)
N = 0 to 128 (decimal)
TABLE 5-1:
VOLATILE WIPER VALUE VS.
WIPER POSITION MAP
Wiper Setting
7-bit Pot 8-bit Pot
Properties
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
081
W = N
040h
080h
W = N (Mid-Scale)
W = N
03Fh
001h
07Fh
001
000h
000h
Zero Scale (W = B)
Decrement command ignored
DS22060B-page 38
© 2008 Microchip Technology Inc.
MICROCHIP [ MICROCHIP ]
