CAT5271ZI-00-GT3 ONSEMI [ON Semiconductor], CAT5271ZI-00-GT3 Datasheet - Page 11

• Manufacturer Part Number: CAT5271ZI-00-GT3
• Description: Dual 256-Position I2C Compatible Digital Potentiometer
• Manufacturer: ONSEMI [ON Semiconductor]

INSTRUCTION AND REGISTER DESCRIPTION
SLAVE ADDRESS BYTE
is called the Slave Address Byte. The most significant seven
bits of the slave address are a device type identifier. For the
CAT5271, these bits are fixed at 0101111. The following bit
(R/W) selects between a Read or a Write operation. If the bit
is logic high, then a Read instruction is performed. If the bit
is low, then the Write command is executed.
INSTRUCTION BYTE
bytes in length. The basic sequence of the two instructions
is illustrated in Table 11 and 12.
Write Operation
selects between the potentiometer 1 and 2: a logic low is for
the potentiometer 1, and a logic high is for potentiometer 2.
causes an open circuit at terminal A while shorting the wiper
terminal W to terminal B. The “shutdown” operation does
not change the contents of the wiper register. When the
shutdown bit, SD, goes back to a logic low, the previous
wiper position is restored. Also during shutdown, new
settings can be programmed. As soon as the device is
returned from shutdown, the wiper position is set according
to the wiper register value.
Legend
SDA
S
A
R
SDA
T
T
Table 11. Write
Table 12. READ
The first byte sent to the CAT5271 from the master/processor
Write and Read instructions are respectively three and two
In the write instruction, the second byte first bit (A0)
The following bit (SD) is the shutdown bit. A logic high
S
S
A
R
T
T
S = Start
P = Stop
A = Acknowledge
D = Data bit
R = Read (bit is 1 for Read instruction)
W = Write (bit is 0 for Write instruction)
S
0
0
Slave Address Byte
1 0
1
Slave Address Byte
0
0
0
Slave Address Byte
1 0
1
1 1
Slave Address Byte
1
0
1
1 1
1
1
1
1
1
1
R/W
1
1 1
W
1
A
C
K
R/W
A
R
A0
A0
A
C
K
A
SD
SD
Instruction Byte
D7
D7
Instruction Byte
X
X
http://onsemi.com
X
X
D6
D6
X
X
X X X
X
11
D5
D5
X
care bits.
Read Operation
the acknowledgment of the slave address byte. Data is
transmitted over the serial bus in sequences.
Read command. The addressed channel is the one that is
previously selected in the write mode. If it desired to read the
potentiometer wiper register values of both channels, the
first potentiometer must be addressed in write mode and
then change to read mode to read the first channel value.
After that, the user must return the device to write mode with
the second potentiometer selected and read the second
potentiometer wiper register value in read mode. It is not
necessary for users to issue the third data byte in write mode
for subsequent read operation.
Wiper Control
(WCR). The Wiper Control Register output is decoded to
select one of 256 switches along its resistor array. The
contents of the WCR may be written by the host via Write
instruction.
loses its contents when the CAT5271 is powered−down.
Upon power−up, the wiper is set to midscale and may be
repositioned anytime after the power has become stable.
The remainder of the bits in the instruction byte are don’t
In the read mode, the data byte follows immediately after
There is no potentiometer channel selection bit in the
The CAT5271 contains two 8−bit Wiper Control Register
The Wiper Control Registers are a volatile register that
X
D4
D4
A0 = Potentiometer Channel (1 or 2) Select Bit
SD = Shut Down:
X = Don’t Care
Data Byte
Data Byte
C
A
K
A
D7
D7
0: normal operation
1: wiper is parked at B terminal and terminal A
is open circuit.
D3
D3
D6
D6
D2
D2
D5
D5
Data Byte
D4
Data Byte
D4
D1
D1
D3
D3
D0
D0
D2
D2
N
A
C
K
D1
A
D1
D0
D0
O
S
T
P
P
A
A
C
K
O
S
T
P
P