CAT5409_13 Datasheet, PDF (9/15 Pages) ON Semiconductor – Quad Digital Potentiometer (POT)

CAT5409
INSTRUCTION AND REGISTER DESCRIPTION
Slave Address Byte
The first byte sent to the CAT5409 from the master/
processor is called the Slave Address Byte. The most
significant four bits of the Device Type address are a device
type identifier. These bits for the CAT5409 are fixed at
0101[B] (refer to Figure 8).
The next four bits, A3 − A0, are the internal slave address
and must match the physical device address which is defined
by the state of the A3 − A0 input pins for the CAT5409 to
successfully continue the command sequence. Only the
device which slave address matches the incoming device
address sent by the master executes the instruction. The A3
− A0 inputs can be actively driven by CMOS input signals
or tied to V_CC or V_SS.
Instruction Byte
The next byte sent to the CAT5409 contains the
instruction and register pointer information. The four most
significant bits used provide the instruction opcode I [3:0].
The R1 and R0 bits point to one of the four data registers of
each associated potentiometer. The least two significant bits
point to one of four Wiper Control Registers. The format is
shown in Figure 9.
Table 11. DATA REGISTER SELECTION
Data Register Selected
R1
R0
DR0
0
0
DR1
0
1
DR2
1
0
DR3
1
1
Device Type
Identifier
Slave Address
ID3
0
(MSB)
I3
(MSB)
ID2
ID1
ID0
A3
A2
1
0
1
Figure 8. Identification Byte Format
Instruction
Opcode
Data Register
Selection
I2
I1
I0
R1
R0
Figure 9. Instruction Byte Format
A1
A0
(LSB)
WCR/Pot Selection
P1
P0
(LSB)
WIPER CONTROL AND DATA REGISTERS
Wiper Control Register (WCR)
The CAT5409 contains four 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 CAT5409 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 5 ms.
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
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