AD7992

–12–

REV. PrH

PRELIMINARYTECHNICAL DATA

INTERNAL REGISTER STRUCTURE

The AD7992 contains eleven internal registers, as shown

in Figure 9, that are used to store conversion results, high

and low conversion limits, and to configure and control

the device. Ten are data registers and one is an address

pointer register.

Figure 9. AD7992 Register Structure

Each data register has an address which is pointed to by

the Address Pointer register when communicating with it.

The Conversion Result Register is the only data register

that is read only.

Table II. Address Pointer Register

C4

C3

C2

C1

P3

P2

P1

P0

0000

Register Select

Table III. AD7992 Register Addresses

P3

P2

P1

P0

Registers

0

0

0

0

Conversion Result Register (Read)

0

0

0

1

Alert Status Register (Read/Write)

0

0

1

0

Configuration Register (Read/Write)

0

0

1

1

Cycle Timer Register (Read/Write)

0

1

0

0

0

1

0

1

0

1

1

0

Hysteresis Reg CH1 (Read/Write)

0

1

1

1

1

0

0

0

1

0

0

1

Hysteresis Reg CH2 (Read/Write)

ADDRESS POINTER REGISTER

The Address Pointer register itself does not have, nor does

it require, an address, as it is the register to which the first

data byte of every Write operation is written automatically.

The Address Pointer Register is an 8-bit register in which

the four LSBs are used as pointer bits to store an address

that points to one of the data registers of the AD7992,

while the four MSBs are used as command bits when us-

ing Mode 2 (see Modes of Operation section). The first

byte following each write address is the address of one of

the data registers, which is stored in the Address Pointer

Register, and selects the data register to which subsequent

data bytes are written. Only the four LSBs of this register

are used to select a data register. On Power up the Ad-

dress Point register contains all 0’s, therefore it is pointing

to the Conversion Result Register.

CONFIGURATION

REGISTER

ADDRESS

POINTER

REGISTER

SERIAL BUS INTERFACE

SDA

SCL

D

A

T

A

DATALOW

REGISTER CH2

DATAHIGH

REGISTER CH2

DATALOW

REGISTER CH1

HYSTERESIS

REGISTER CH1

DATAHIGH

REGISTER CH1

CYCLE TIMER

REGISTER

ALERT STATUS

REGISTER

CONVERSION

RESULT REGISTER

HYSTERESIS

REGISTER CH2

CONFIGURATION REGISTER

The Configuration Register is an 8-bit read/write register that is used to set the operating modes of the AD7992. The

MSB is used, and is a Don’t Care bit. The bit functions are outlined in Table IV.

Table IV.

Configuration Register Bit Function Description

D7

D6

D5

D4

D3

D2

D1

D0

DONTC

Single/Dual CH2

CH1

F L T R

ALERT EN

BUSY/

ALERT

ALERT/BUSY POLARITY

0*

0*

0*

0*

1*

0*

0*

0*

*Default settings at Power-up