7
FN8161.5
April 9, 2014
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Instruction and Register Description
Device Addressing
WIPER COUNTER REGISTER (WCR)
The X9118 contains a Wiper Counter Register (see Table 4)
for the XDCP potentiometer. The WCR is equivalent to a
serial-in, parallel-out register/counter with its outputs
decoded to select one of 1024 switches along its resistor
array. The contents of the WCR can be altered in one of
three ways:
1. It may be written directly by the host via the write Wiper
Counter Register instruction (serial load).
2. It may be written indirectly by transferring the contents of
one of four associated Data Registers via the XFR Data
register.
3. It is loaded with the contents of its Data Register zero
(R0) upon power-up.
The Wiper Counter Register is a volatile register; that is,
contents are lost when the X9118 is powered down. Although
the register is automatically loaded with the value in DR0
upon power-up, this may be different from the value present at
power-down. Power-up guidelines are recommended to
ensure proper loadings of the DR0 value into the WCR.
DATA REGISTERS (DR)
The potentiometer has four 10-bit non-volatile Data
Registers. These can be read or written directly by the host.
Data can be transferred between any of the four data
registers and the Wiper Counter Register. All operations
changing data in one of the Data Registers is a nonvolatile
operation and will take a maximum of 10ms.
If the application does not require storage of multiple
settings for the potentiometer, the Data Registers can be
used as regular memory locations for system parameters or
user preference data.
Bit 9 to Bit 0 are used to store one of the 1024 wiper position
(0 ~1023).
Four of the six instructions are four bytes in length. These
instructions are:
• Read Wiper Counter Register – Read the current wiper
position of the potentiometer.
• Write Wiper Counter Register – Change current wiper
position of the potentiometer.
• Read Data Register – Read the contents of the selected
Data Register.
• Write Data Register – Write a new value to the selected
Data Register.
The basic sequence of the four byte instructions is illustrated
in Figure 3. These four-byte instructions exchange data
between the WCR and one of the Data Registers. A transfer
from a data register to a WCR is essentially a write to a static
RAM, with the static RAM controlling the wiper position. The
response of the wiper to this action will be delayed by t
WRL
. A
transfer from the WCR (current wiper position), to a data
register is a write to nonvolatile memory and takes a minimum
of t
WR
to complete. The transfer can occur between the
potentiometer and one of its associated registers.
Two instructions (see Figure 4) require a two-byte sequence
to complete. These instructions transfer data between the
host and the X9118; either between the host and one of the
Data Registers or directly between the host and the Wiper
Counter Register. These instructions are:
• XFR Data Register to Wiper Counter Register – This
transfers the contents of one specified Data Register to
the Wiper Counter Register.
• XFR Wiper Counter Register to Data Register –This
transfers the contents of the specified Wiper Counter
Register to the specified Data Register.
Refer to “Instruction Format” on page 8 for more details.
Other
POWER-UP AND POWER-DOWN REQUIREMENTS
At all times, the V+ voltage must be greater than or equal to
the voltage at R
H
or R
L
, and the voltage at R
H
or R
L
must be
greater than or equal to the voltage at V-. During power-up
and power-down, V
CC
, V+, and V- must reach their final
values within 1ms of each other.
TABLE 4. WIPER CONTROL REGISTER, WCR (10-BIT), WCR9 TO WCR0: USED TO STORE THE CURRENT WIPER POSITION (VOLATILE, V)
WCR9 WCR8 WCR7 WCR6 WCR5 WCR4 WCR3 WCR2 WCR1 WCR0
VVVVVVVVVV
(MSB) (LSB)
TABLE 5. DATA REGISTER, DR (10-BIT), BIT 9 TO BIT 0: USED TO STORE WIPER POSITIONS OR DATA (NON-VOLATILE, NV)
BIT 9 BIT 8 BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
NV NV NV NV NV NV NV NV NV NV
MSB LSB
X9118
