X9241A
Figure 8. Detailed Potentiometer Block Diagram
Serial Data Path
Serial
Bus
Input
V /R
H
H
From Interface
Circuitry
Register 0
Register 2
Register 1
Parallel
Bus
Input
8
6
C
o
u
n
t
e
r
Wiper
Counter
Register
Register 3
D
e
c
o
d
e
2
INC/DEC
Logic
UP/DN
If WCR = 00[H] then V /R = V /R
L
W
W
L
UP/DN
If WCR = 3F[H] then V /R = V /R
V /R
W
W
H
H
Modified SCL
L
L
CLK
DW
Cascade
Control
Logic
V
/R
W
W
CM
Cascade Mode
The state of DW enables or disables the wiper. When
the DW bit of the WCR is set to “0” the wiper is enabled;
when set to “1” the wiper is disabled. If the wiper is
disabled, the wiper terminal will be electrically isolated
and float.
The X9241A provides a mechanism for cascading the
arrays. That is, the sixty-three resistor elements of one
array may be cascaded (linked) with the resistor
elements of an adjacent array. The V /R of the higher
L
L
order array must be connected to the V /R of the
lower order array (See Figure 9).
H
H
When operating in cascade mode V /R , V /R and
H
H
L
L
the wiper terminals of the cascaded arrays must be
electrically connected externally. All but one of the
wipers must be disabled. The user can alter the wiper
position by writing directly to the WCR or indirectly by
transferring the contents of the Data Registers to the
WCR or by using the Increment/Decrement command.
Cascade Control Bits
The data byte, for the three-byte commands, contains 6
bits (LSBs) for defining the wiper position plus two high
order bits, CM (Cascade Mode) and DW (Disable
Wiper, normal operation).
When using the Increment/Decrement command the
wiper position will automatically transition between
arrays. The current position of the wiper can be
determined by reading the WCR registers; if the DW bit
is “0”, the wiper in that array is active. If the current
wiper position is to be maintained on power-down a
global XFR WCR to Data Register command must be
issued to store the position in NV memory before
power-down.
The state of the CM bit (bit 7 of WCR) enables or
disables cascade mode. When the CM bit of the WCR
is set to “0” the potentiometer is in the normal operation
mode. When the CM bit of the WCR is set to “1” the
potentiometer is cascaded with its adjacent higher
order potentiometer. For example; if bit 7 of WCR2 is
set to “1”, pot 2 will be cascaded to pot 3.
Characteristics subject to change without notice. 8 of 18
REV 1.1.13 12/09/02
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