CAT5221WI-25 Datasheet, PDF (9/16 Pages) ON Semiconductor – Dual Digitally Programmable Potentiometer with 64 Taps and I2C Interface

CAT5221
WIPER CONTROL AND DATA REGISTERS
Wiper Control Register (WCR)
The CAT5221 contains two 6-bit Wiper Control
Registers, one for each potentiometer. The Wiper
Control Register output is decoded to select one of 64
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 CAT5221 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 6-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.
Instructions
Four of the nine 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
— Write Data Register – write a new value to the
selected Data Register
The basic sequence of the three byte instructions is
illustrated in Figure 8. These three-byte instructions
Table 3. Instruction Set
Instruction
Read Wiper Control
Register
Write Wiper Control
Register
Read Data Register
Instruction Set
WCR0/
I3 I2 I1 I0 0 P0
R1
1 0 0 1 0 1/0 0
1 0 1 0 0 1/0 0
1 0 1 1 0 1/0 1/0
Write Data Register
1 1 0 0 0 1/0 1/0
XFR Data Register to
Wiper Control Register
1 1 0 1 0 1/0 1/0
XFR Wiper Control
Register to Data Register
1 1 1 0 0 1/0
1/0
Global XFR Data Registers
to Wiper Control Registers
0
0
0
1
0
0
1/0
Global XFR Wiper Control
Registers to Data Register
10000
0
1/0
Increment/Decrement
Wiper Control Register
0 0 1 0 0 1/0 0
Note: 1/0 = data is one or zero
R0 ^Operation
0
Read the contents of the Wiper Control
Register pointed to by P0
0
Write new value to the Wiper Control Register
pointed to by P0
1/0
Read the contents of the Data Register
pointed to by P0 and R1-R0
1/0
Write new value to the Data Register pointed
to by P0 and R1-R0
Transfer the contents of the Data Register
1/0 pointed to by P0 and R1-R0 to its associated
Wiper Control Register
Transfer the contents of the Wiper Control
1/0 Register pointed to by P0 to the Data
Register pointed to by R1-R0
Transfer the contents of the Data Registers
1/0 pointed to by R1-R0 of all four pots to their
respective Wiper Control Registers
Transfer the contents of both Wiper Control
1/0 Registers to their respective data Registers
pointed to by R1-R0 of all four pots
0
Enable Increment/decrement of the Control
Latch pointed to by P0
© 2008 SCILLC. All rights reserved.
9
Characteristics subject to change without notice
Doc. No. MD-2113 Rev. L