CAT5251 Datasheet, PDF (8/15 Pages) Catalyst Semiconductor – Quad Digitally Programmable Potentiometer (DPP) with 256 Taps and SPI Interface

CAT5251
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 ^{¯C¯S¯} 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
Four 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
— Write Data Register – write a new value to the
selected Data Register
— Read Status – Read the status of the WIP bit which
when set to "1" signifies a write cycle is in progress.
Table 3. Instruction Set
Note: 1/0 = data is one or zero
Instruction Set
Operations
Instruction
WCR1/ WCR0/
I3 I2 I1 I0 R1 R0 P1
P0
Read Wiper Control
Register
Write Wiper Control
Register
Read Data Register
1 0 0 1 0 0 1/0
1 0 1 0 0 0 1/0
1 0 1 1 1/0 1/0 1/0
Write Data Register
1 1 0 0 1/0 1/0 1/0
XFR Data Register to
Wiper Control Register
1 1 0 1 1/0 1/0 1/0
XFR Wiper Control
Register to Data Register
1 1 1 0 1/0 1/0 1/0
Global XFR Data Registers
to Wiper Control Registers
0
0
0
1 1/0 1/0
0
1/0
Read the contents of the Wiper Control Register
pointed to by P1-P0
1/0
Write new value to the Wiper Control Register pointed
to by P1-P0
1/0
Read the contents of the Data Register pointed to by
P1-P0 and R1-R0
1/0
Write new value to the Data Register pointed to by
P1-P0 and R1-R0
Transfer the contents of the Data Register pointed to
1/0 by P1-P0 and R1-R0 to its associated Wiper Control
Register
Transfer the contents of the Wiper Control Register
1/0 pointed to by P1-P0 to the Data Register pointed to by
R1-R0
Transfer the contents of the Data Registers pointed to by
0 R1-R0 of all four pots to their respective Wiper Control
Registers
Global XFR Wiper Control
Registers to Data Register
100
0 1/0 1/0
0
Increment/Decrement
Wiper Control Register
0 0 1 0 0 0 1/0
Transfer the contents of both Wiper Control Registers
0 to their respective data Registers pointed to by R1-R0
of all four pots
1/0
Enable Increment/decrement of the Control Latch
pointed to by P1-P0
Read Status (WIP bit)
010 1 0 0 0
1 Read WIP bit to check internal write cycle status
Doc. No. MD-2017 Rev. H
8
© 2009 SCILLC. All rights reserved.
Characteristics subject to change without notice