cat5270 ON Semiconductor, cat5270 Datasheet - Page 7

• Manufacturer Part Number: cat5270
• Description: Dual Digitally Programmable Potentiometers Dpp With 256 Taps & I2c Compatible Interface
• Manufacturer: ON Semiconductor

Instruction and Register Description
Instruction Byte
instruction and register pointer information. The four most
significant bits used provide the instruction opcode I3 − I0.
Instructions
Instructions are three bytes in length. These instructions are:
− Read Wiper Control Register – read the current wiper
− Write Wiper Control Register – change current wiper
− Increment/Decrement Wiper Control Register –
illustrated in Figure 8.
Write Operation
condition and the slave address information to the Slave
device. After the Slave generates an acknowledge, the
Master sends the instruction byte that defines the requested
operation of CAT5270. The instruction byte consists of a
seven−bit opcode followed by pot/register selection bit.
After receiving another acknowledge from the Slave, the
Master device transmits the data to be written into the
selected register. The CAT5270 acknowledges once more
and the Master generates the STOP condition.
10. 1/0 = data is one or zero
Table 10. INSTRUCTION SET
Read Wiper Control Register
Write Wiper Control Register
Increment/Decrement Wiper
Control Register
The next byte sent to the CAT5270 contains the
The basic sequence of the three byte instructions is
In the Write mode, the Master device sends the START
position of the selected potentiometer in the WCR
position in the WCR of the selected potentiometer
change step by step the current wiper position in the
WCR of the selected potentiometer
Instruction
(MSB)
I3
I2
I3
1
1
0
Instruction
Opcode
I2
0
0
0
I1
I1
0
1
1
Figure 6. Instruction Byte Format
Instruction Set (Note 10)
I0
1
0
0
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F2
I0
0
0
0
F1
7
0
0
0
Increment/Decrement Command
10). The Increment/Decrement command is different from
the other commands. Once the instruction is issued and the
CAT5270 has responded with an acknowledge, the master
can clock the selected wiper up and/or down in one segment
steps; thereby providing a fine tuning capability to the host.
For each SCL clock pulse (t
selected wiper will move one resistor segment towards the
R
is LOW, the selected wiper will move one resistor segment
towards the R
See Instructions format for more details.
Wiper Control Register (WCR)
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 two ways: it may be written by the host via Write
Wiper Control Register instruction; or it can be modified one
step at a time by the Increment/decrement instruction (see
Instruction section for more details).
its contents when the CAT5270 is powered−down. Upon
power−up, the wiper is set to midspan and may be
repositioned anytime after the power has become stable.
H
0
F0
The last command is Increment/Decrement (Figures 9 and
The CAT5270 contains two 8−bit Wiper Control
The Wiper Control Register is a volatile register that loses
0
0
0
terminal. Similarly, for each SCL clock pulse while SDA
WCR/P
1/0
1/0
1/0
0
L
P
0
1
terminal.
Read the contents of the Wiper Control
Register pointed to by P
Write new value to the Wiper Control
Register pointed to by P
Enable Increment/decrement of the
Control Latch pointed to by P
0
HIGH
) while SDA is HIGH, the
Operation
Set R0 wiper position
Set R1 wiper position
WCR Pot
Selector
(LSB)
P0
WCR