X95820 Datasheet, PDF (9/12 Pages) Intersil Corporation – Dual Digital Controlled Potentiometers

X95820
Principles of Operation
The X95820 in as integrated circuit incorporating two DCPs
with their associated registers, non-volatile memory, and a 2-
wire serial interface providing direct communication between
a host and the potentiometers and memory.
DCP Description
Each DCP is implemented with a combination of resistor
elements and CMOS switches. The physical ends of each
DCP are equivalent to the fixed terminals of a mechanical
potentiometer (RH and RL pins). The RW pin of each DCP is
connected to intermediate nodes, and is equivalent to the
wiper terminal of a mechanical potentiometer. The position
of the wiper terminal within the DCP is controlled by an 8-bit
volatile Wiper Register (WR). Each DCP has its own WR.
When the WR of a DCP contains all zeroes (WR<7:0>: 00h),
its wiper terminal (RW) is closest to its “Low” terminal (RL).
When the WR of a DCP contains all ones (WR<7:0>: FFh),
its wiper terminal (RW) is closest to its “High” terminal (RH).
As the value of the WR increases from all zeroes (00h) to all
ones (255 decimal), the wiper moves monotonically from the
position closest to RL to the closest to RH. At the same time,
the resistance between RW and RL increases monotonically,
while the resistance between RH and RW decreases
monotonically.
While the X95820 is being powered up, all two WRs are
reset to 80h (128 decimal), which locates RW roughly at the
center between RL and RH. Soon after the power supply
voltage becomes large enough for reliable non-volatile
memory reading, the X95820 reads the value stored on two
different non-volatile Initial Value Registers (IVRs) and loads
them into their corresponding WRs.
The WRs and IVRs can be read or written directly using the
2-wire serial interface as described in the following sections.
Memory Description
The X95820 contains eight non-volatile bytes. they are
accessed by 2-wire interface operations with Address Bytes
0 through 7 decimal. The first two non-volatile bytes at
addresses 0 and 1 contain the initial value loaded at power-
up into the volatile Wiper Registers (WRs) of DCP0 and
DCP1 respectively. Bytes at addresses 2, 3, 4, 5, and 6 are
available to the user as general purpose registers. The byte
at address 7 is reserved; the user should not write to it, and
its value should be ignored if read.
The volatile WR, and the non-volatile Initial Value Register
(IVR) of a DCP are accessed with the same Address Byte.
A volatile byte at address 8 decimal, controls what byte is
read or written when accessing DCP registers: the WR, the
IVR, or both.
When the byte at address 8 is all zeroes, which is the default
at power up:
• A read operation to addresses 0 or 1 outputs the value of
the non-volatile IVRs.
• A write operation to addresses 0 or 1 writes the same
value to the WR and IVR of the corresponding DCP.
When the byte at address 8 is 80h (128 decimal):
• A read operation to addresses 0 or 1 outputs the value of
the volatile WR.
• A write operation to addresses 0 or 1only writes to the
corresponding volatile WR.
It is not possible to write to an IVR without writing the same
value to its corresponding WR.
00h and 80h are the only values that should be written to
address 8. All other values are reserved and must not be
written to address 8.
To access the general purpose bytes at addresses 2, 3, 4, 5,
or 6, the value at address 8 must be all zeros.
The X95820 is pre-programmed with 80h in the two IVRs.
TABLE 1. MEMORY MAP
ADDRESS
NON-VOLATILE
VOLATILE
8
-
Access Control
7
Reserved
6
General Purpose
5
4
3
2
Not Available
1
IVR1
0
IVR0
WR1
WR0
WR: Wiper Register, IVR: Initial value Register.
2-Wire Serial Interface
The X95820 supports a bidirectional bus oriented protocol.
The protocol defines any device that sends data onto the
bus as a transmitter and the receiving device as the receiver.
The device controlling the transfer is a master and the
device being controlled is the slave. The master always
initiates data transfers and provides the clock for both
transmit and receive operations. Therefore, the X95820
operates as a slave device in all applications.
All communication over the 2-wire interface is conducted by
sending the MSB of each byte of data first.
Protocol Conventions
Data states on the SDA line can change only during SCL
LOW periods. SDA state changes during SCL HIGH are
reserved for indicating START and STOP conditions (See
Figure 15). On power up of the X95820 the SDA pin is in the
input mode.
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FN8212.1
September 26, 2005