CAT5269_13 Datasheet, PDF (9/15 Pages) ON Semiconductor – Dual Digital Potentiometer (POT)

CAT5269
INSTRUCTION AND REGISTER DESCRIPTION
Slave Address Byte
The first byte sent to the CAT5269 from the
master/processor is called the Slave Address Byte. The most
significant four bits of the slave address are a device type
identifier. These bits for the CAT5269 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 CAT5269 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 CAT5269 contains the
instruction and register pointer information. The four most
significant bits used provide the instruction opcode I3 − I0.
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 12. DATA REGISTER SELECTION
Data Register Selected
R1
R0
DR0
0
0
DR1
0
1
SLAVE
ADDRESS
INSTRUCTION
BYTE
S
T
BUS ACTIVITY:
MASTER
A
R
T
SDA LINE S
S
T
DR1 WCRDATA
O
P
P
A
A
A
C
C
C
K
K
K
Figure 7. Write Timing
Device Type
Identifier
Slave Address
ID3
0
(MSB)
ID2
ID1
ID0
A3
A2
1
0
1
Figure 8. Identification Byte Format
Instruction
Opcode
Data Register
Selection
A1
A0
(LSB)
WCR/Pot Selection
I3
I2
(MSB)
I1
I0
R1
R0
Figure 9. Instruction Byte Format
P1
P0
(LSB)
WIPER CONTROL AND DATA REGISTERS
Wiper Control Register (WCR)
The CAT5269 contains two 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 CAT5269 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.
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