Philips Semiconductors

Product data

NE1618

Temperature monitor for microprocessor systems

2002 Jan 04

7

FUNCTIONAL DESCRIPTION

Serial bus interface

The NE1618 can be connected to a compatible 2-wire serial

interface System Management Bus (SMBus) as a slave device

under the control of a master device, using two device terminals

SCLK and SDATA. The controller will provide a clock signal to the

device SCLK pin and write/read data to/from the device through the

device SDATA pin. External pull-up resistors, about 10 k

Ω each,

are needed for these two terminals due to the open drain circuitry.

Data of 8-bit digital byte or word are used for communication

between the controller and the device using SMBus protocols which

will be described more in the SMBus interface section. The

operation of the device to the bus is described with details in the

following sections.

Slave address

The 7-bit address data of the NE1618 on the bus is defined by

three-level logical connections applied to the device address pins

ADD0 and ADD1. They are either opened or connected directly to

equal to or less than 2 k

Ω. The selectable addresses are listed in

Table 1. Any one of those nine combinations can be used for any

device and more than one devices can reside on the same bus

without conflict. Notice that because the state of the device address

pins is sampled and latched not only at the power-up step but also

at starting point of every conversion, the address connections must

be permanently existent.

Table 1. Device slave address

ADD0 pin

ADD1 pin

7-BIT ADDRESS DATA

GND

GND

0011 000

GND

NC

0011 001

GND

0011 010

NC

GND

0101 001

NC

NC

0101 010

NC

0101 011

GND

1001 100

NC

1001 101

1001 110

1. NC = Not Connected.

Registers

The NE1618 contains a number of registers which names,

commands, power-on reset (POR) status and functions are listed in

Table 2. It includes:

NE1618

comparisons

The registers are used to store either programmable data for setting

device operation or resultant data from device measurement. Data

are stored in registers by 8-bit digital byte, either in 2’s complement

format for temperature-related data or in straight format for others.

The register command byte is used to addressing the register in

SMBus communication. Writing and reading registers will be

performed on the SMBus by a controller. The registers are divided

into two groups: only-read registers named with a prefix of R– and

only-write registers named with a prefix of W– (including the

one-shot register OSHT). You should write programmable data to

the only-write registers and read data from the only-read registers.

Attempting to write to any R– register or read from any W– register

will produce an invalid result: the writing data would be ignored, the

reading data would be equal to FFh. Some of registers are in pair

representing a same item for different bus operations: read and

write, for example, RC and WC are related to the device

configuration, one for reading and the other for writing.

The reserved registers are used only at the manufacturer for test

purposes.