CAT5270 Datasheet, PDF (7/10 Pages) ON Semiconductor – Dual Digitally Programmable Potentiometers (DPP) with 256 Taps & I2C Compatible Interface

CAT5270
Instruction and Register Description
Instruction Byte
The next byte sent to the CAT5270 contains the
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
position of the selected potentiometer in the WCR
− Write Wiper Control Register – change current wiper
position in the WCR of the selected potentiometer
− Increment/Decrement Wiper Control Register –
change step by step the current wiper position in the
WCR of the selected potentiometer
The basic sequence of the three byte instructions is
illustrated in Figure 8.
Write Operation
In the Write mode, the Master device sends the START
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.
Instruction
Opcode
Increment/Decrement Command
The last command is Increment/Decrement (Figures 9 and
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_HIGH) while SDA is HIGH, the
selected wiper will move one resistor segment towards the
R_H terminal. Similarly, for each SCL clock pulse while SDA
is LOW, the selected wiper will move one resistor segment
towards the R_L terminal.
See Instructions format for more details.
Wiper Control Register (WCR)
The CAT5270 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 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).
P
WCR
0
Set R0 wiper position
1
Set R1 wiper position
The Wiper Control Register is a volatile register that loses
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.
WCR Pot
Selector
I3
I2
(MSB)
I1
I0
0
0
Figure 6. Instruction Byte Format
0
P0
(LSB)
Table 10. INSTRUCTION SET
Instruction Set (Note 10)
Instruction
I3 I2 I1 I0 F2 F1 F0 WCR/P
Operation
Read Wiper Control Register 1 0 0 1 0 0 0
1/0
Read the contents of the Wiper Control
Register pointed to by P
Write Wiper Control Register 1 0 1 0 0 0 0
1/0
Write new value to the Wiper Control
Register pointed to by P
Increment/Decrement Wiper 0 0 1 0 0 0 0
Control Register
1/0
Enable Increment/decrement of the
Control Latch pointed to by P
10. 1/0 = data is one or zero
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