X9421 Xicor, X9421 Datasheet - Page 6

• Manufacturer Part Number: X9421
• Description: Single Digitally Controlled (XDCP) Potentiometer
• Manufacturer: Xicor

Figure 1. Detailed Potentiometer Block Diagram
X9421
Write in Process
The contents of the Data Registers are saved to
nonvolatile memory when the CS pin goes from LOW
to HIGH after a complete write sequence is received by
the device. The progress of this internal write operation
can be monitored by a Write In Process bit (WIP). The
WIP bit is read with a Read Status command.
INSTRUCTIONS
Address/Identification (ID) Byte
The first byte sent to the X9421 from the host, following
a CS going HIGH to LOW, is called the Address or
Identification byte. The most significant four bits of the
slave address are a device type identifier, for the
X9421 this is fixed as 0101[B] (refer to Figure 2).
The least significant bit in the ID byte selects one of
two devices on the bus. The physical device address is
defined by the state of the A
compares the serial data stream with the address input
state; a successful compare of the address bit is
required for the X9421 to successfully continue the
command sequence. The A
driven by a CMOS input signal or tied to V
The remaining three bits in the ID byte must be set to
110.
REV 1.1.6 8/1/02
IF WCR = 00[H] THEN V
IF WCR = 3F[H] THEN V
Serial Data Path
From Interface
Circuitry
W
W
= V
= V
L
H
0
0
REGISTER 2
Register 0
input can be actively
input pin. The X9421
CC
8
or V
SS
www.xicor.com
REGISTER 3
Register 1
.
Modified SCK
UP/DN
Figure 2. Address/Identification Byte Format
Instruction Byte
The next byte sent to the X9421 contains the
instruction and register pointer information. The four
most significant bits are the instruction. The next two
bits point to one of four Data Registers. The format is
shown below in Figure 3.
Figure 3. Instruction Byte Format
6
0
UP/DN
CLK
Parallel
Serial
Bus
Input
Bus
Input
I3
Device Type
Identifier
Register
INC/DEC
Counter
1
(WCR)
Instructions
Wiper
Logic
I2
0
Characteristics subject to change without notice.
I1
1
C
O
U
N
T
E
R
D
E
C
O
D
E
I0
1
Register
R1
Select
1
R0
Device Address
0
0
A0
0
V
V
V
H
L
W
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