X9421 datasheet(6/20 Pages) RENESAS

6 / 20 page

X9421

FN8196 Rev.1.00

Page 6 of 20

January 14, 2009

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 A0 input pin. The X9421 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 A0 input can be actively

driven by a CMOS input signal or tied to VCC or VSS.

The remaining three bits in the ID byte must be set to 110.

Instruction Byte

The next byte sent to the X9421 contains the instruction and

the instruction. The next two bits point to one of four Data

Registers. The format is shown below in Figure 3.

The four high order bits of the instruction byte specify the

operation. The next two bits (R1 and R0) select one of the four

registers that is to be acted upon when a register oriented

instruction is issued. The last two bits are defined as 0.

SERIAL DATA PATH

FROM INTERFACE

CIRCUITRY

SERIAL

BUS

INPUT

PARALLEL

BUS

INPUT

COUNTER

INC/DEC

LOGIC

UP/DN

CLK

MODIFIED SCK

UP/DN

IF WCR = 00[H] THEN VW = VL

IF WCR = 3F[H] THEN VW = VH

WIPER

(WCR)

FIGURE 1. DETAILED POTENTIOMETER BLOCK DIAGRAM

0A0

DEVICE TYPE

IDENTIFIER

DEVICE ADDRESS

FIGURE 2. ADDRESS/IDENTIFICATION BYTE FORMAT

SELECT

INSTRUCTIONS

FIGURE 3. INSTRUCTION BYTE FORMAT

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