X9241
DETAILED OPERATION
The WCR is a volatile register; that is, its contents are
lost when the X9241 is powered-down. Although the
register is automatically loaded with the value in R0
upon power-up, it should be noted this may be different
from the value present at power-down.
2
All four E POT potentiometers share the serial interface
and share a common architecture. Each potentiometer
is comprised of a resistor array, a wiper counter register
and four data registers. A detailed discussion of the
register organization and array operation follows.
Data Registers
Each potentiometer has four nonvolatile data registers.
These can be read or written directly by the host and
data can be transferred between any of the four data
registers and the WCR. It should be noted all operations
changing data in one of these registers is a nonvolatile
operation and will take a maximum of 10ms.
Wiper Counter Register
TheX9241containsfourwipercounterregisters(WCR),
2
one for each E POT potentiometer. The WCR can be
envisionedasa6-bitparallelandserialloadcounterwith
its outputs decoded to select one of sixty-four switches
along its resistor array. The contents of the WCR can be
altered in four ways: it may be written directly by the host
via the Write WCR instruction (serial load); it may be
written indirectly by transferring the contents of one of
fourassociateddataregistersviatheXFRDataRegister
instruction (parallel load); it can be modified one step at
a time by the Increment/ Decrement instruction; finally,
itisloadedwiththecontentsofitsdataregisterzero(R0)
upon power-up.
If the application does not require storage of multiple
settings for the potentiometer, these registers can be
used as regular memory locations that could possibly
store system parameters or user preference data.
Figure 8. Detailed Potentiometer Block Diagram
SERIAL DATA PATH
V
SERIAL
BUS
INPUT
H
FROM INTERFACE
CIRCUITRY
REGISTER 0
REGISTER 2
REGISTER 1
PARALLEL
BUS
INPUT
8
6
C
O
U
N
T
WIPER
COUNTER
REGISTER
REGISTER 3
E
R
D
E
C
O
D
E
2
INC/DEC
LOGIC
IF WCR = 00[H] THEN VW = VL
IF WCR = 3F[H] THEN VW = VH
UP/DN
UP/DN
V
V
L
MODIFIED SCL
CLK
DW
CASCADE
CONTROL
W
LOGIC
CM
3864 ILL F15
7
XICOR [ XICOR INC. ]
