9
CAT5251
Document No. 2017, Rev. D
Table 3. Instruction Set
WIPER CONTROL AND DATA REGISTERS
Wiper Control Register (WCR)
The CAT5251 contains four 8-bit Wiper Control
Registers, one for each potentiometer. The Wiper
Control Register output is decoded to select one of
256 switches along its resistor array. The contents of
the WCR can be altered in four ways: it may be written
by the host via Write Wiper Control Register instruction;
it may be written by transferring the contents of one of
four associated Data Registers via the XFR Data
Register instruction; it can be modified one step at a
time by the Increment/decrement instruction (see
Instruction section for more details). Finally, it is
loaded with the content of its data register zero (DR0)
upon power-up.
The Wiper Control Register is a volatile register that
loses its contents when the CAT5251 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.
Data Registers (DR)
Each potentiometer has four 8-bit non-volatile Data
Registers. These can be read or written directly by the
host. Data can also be transferred between any of the
four Data Registers and the associated Wiper Control
Register. Any data changes in one of the Data Registers
is a non-volatile operation and will take a maximum of
5ms.
If the application does not require storage of multiple
settings for the potentiometer; the Data Registers can be
used as standard memory locations for system
parameters or user preference data.
Write in Process
The contents of the Data Registers are saved to
nonvolatile memory when the CS input goes HIGH after
a write sequence is received. The status of the internal
write cycle can be monitored by issuing a Read Status
command to read the Write in Process (WIP) bit.
INSTRUCTIONS
Five of the ten instructions are three bytes in length.
These instructions are:
—Read Wiper Control Register - read the current
wiper position of the selected potentiometer in the WCR
—Write Wiper Control Register - change current
wiper position in the WCR of the selected potentiometer
—Read Data Register - read the contents of the
selected Data Register
Note: 1/0 = data is one or zero
Instruction
Instruction Set
Operation
I3 I2 I1 I0 R1 R0 WCR1/
P1
Read Wiper Control
Register 100100 1/0 1/0Read the contents of the Wiper Control
Register pointed to by P1-P0
Write Wiper Control Register 101000 1/0 1/0Write new value to the Wiper Control
Register pointed to by P1-P0
Read Data Register 10111/01/01/0 1/0Read the contents of the Data Register
pointed to by P1-P0 and R1-R0
Write Data Register 11001/01/01/0 1/0Write new value to the Data Register
pointed to by P1-P0 and R1-R0
XFR Data Register to Wiper
Control Register 11011/01/01/0 1/0Transfer the contents of the Data Register
pointed to by P1-P0 and R1-R0 to its
associated Wiper Control Register
XFR Wiper Control Register
to Data Register 11101/01/01/0 1/0Transfer the contents of the Wiper Control
Register pointed to by P1-P0 to the Data
Register pointed to by R1-R0
Global XFR Data
Registers
to Wiper Control Registers 00011/01/0 0 0 Transfer the contents of the Data Registers
pointed to by R1-R0 of all four pots to their
respective Wiper Control Register
Global XFR Wiper Control
Registers to Data Register 10001/01/0 0 0 Transfer the contents of both Wiper Control
Registers to their respective data Registers
pointed to by R1-R0 of all four pots
Increment/Decrement Wiper
Control Register 001000 1/0 1/0Enable Increment/decrement of the Control
Latch pointed to by P1-P0
WCR0/
P0
Read Status (WIP bit) 010100 0 1 Read WIP bit to check internal
write cycle status