Datasheet

MCP453X/455X/463X/465X
DS22096B-page 40  2008-2013 Microchip Technology Inc.
5.2 Wiper
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 connection, connects the Ter-
minal W (wiper) to Terminal B (wiper setting of 000h). A
full-scale connection, connects the Terminal W (wiper)
to Terminal A (wiper setting of 100h or 80h). In these
configurations, the only resistance between 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). Tabl e 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
WB
CALCULATION
TABLE 5-1: VOLATILE WIPER VALUE VS.
WIPER POSITION MAP
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.
R
WB
R
AB
N
256
--------------R
W
+=
N = 0 to 256 (decimal)
R
WB
R
AB
N
128
--------------R
W
+=
N = 0 to 128 (decimal)
8-bit Device
7-bit Device
Wiper Setting
Properties
7-bit Pot 8-bit Pot
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)
03Fh
001h
07Fh
001
W = N
000h 000h Zero Scale (W = B)
Decrement command ignored
TABLE 5-2: DEFAULT FACTORY
SETTINGS SELECTION
Resistance
Code
Typical
R
AB
Value
Default POR
Wiper Setting
Wiper Code
8-bit 7-bit
-502 5.0 k Mid-scale 80h 40h
-103 10.0 k Mid-scale 80h 40h
-503 50.0 k Mid-scale 80h 40h
-104 100.0 k Mid-scale 80h 40h