REV. 0

ADM1032

–7–

Consecutive

ALERT Register

This value written to this register determines how many out-of-

limit measurements must occur before an

ALERT is generated.

The default value is that one out-of-limit measurement gener-

ates an

ALERT. The max value that can be chosen is 4. The

purpose of this register is to allow the user to perform some filter-

ing of the output. This is particularly useful at the faster two

conversion rates where no averaging takes place.

Table VII.

Number of “Out-of-Limit”

Register Value

Measurements Required

yxxx 000x

1

yxxx 001x

2

yxxx 011x

3

yxxx 111x

4

NOTES

x = Don’t care bit.

y = SMBus timeout bit. Default = 0. See SMBus section for more

information.

SERIAL BUS INTERFACE

Control of the ADM1032 is carried out via the serial bus. The

ADM1032 is connected to this bus as a slave device, under the

control of a master device.

There is a programmable SMBus timeout. When this is enabled

the SMBus will timeout after typically 25 ms of no activity. How-

ever, this feature is not enabled by default. To enable it, set Bit 7

of the Consecutive Alert Register (Addr = 22h).

The ADM1032 supports Packet Error Checking (PEC) and its

use is optional. It is triggered by supplying the extra clock for the

PEC byte. The PEC byte is calculated using CRC-8. The Frame

Check Sequence (FCS) conforms to CRC-8 by the polynomial:

Consult SMBus 1.1 specification for more information

(www.smbus.org).

ADDRESSING THE DEVICE

In general, every SMBus device has a 7-bit device address (except

for some devices that have extended, 10-bit addresses). When

the master device sends a device address over the bus, the slave

device with that address will respond. The ADM1032 is avail-

able with one device address, which is Hex 4C (1001 100).

The serial bus protocol operates as follows:

1. The master initiates data transfer by establishing a START

condition, defined as a high-to-low transition on the serial

data line SDATA, while the serial clock line SCLK remains

high. This indicates that an address/data stream will follow.

All slave peripherals connected to the serial bus respond to

the START condition, and shift in the next eight bits, con-

sisting of a 7-bit address (MSB first) plus an R/

W bit, which

determines the direction of the data transfer, i.e., whether

data will be written to or read from the slave device.

The peripheral whose address corresponds to the transmitted

address responds by pulling the data line low during the low

period before the ninth clock pulse, known as the Acknowl-

edge Bit. All other devices on the bus now remain idle while

the selected device waits for data to be read from or written

Table V. Configuration Register Bit Assignments

Power-On

Bit

Name

Function

Default

7

MASK1

0 =

ALERT Enabled

0

1 =

ALERT Masked

6

RUN/STOP

0 = Run

0

1 = Standby

5–0

Reserved

0

Conversion Rate Register

The lowest four bits of this register are used to program the

conversion rate by dividing the internal oscillator clock by 1, 2,

4, 8, 16, 32, 64, 128, 256, 512, or 1024 to give conversion

times from 15.5 ms (code 0Ah) to 16 seconds (code 00h). This

register can be written to and read back over the SMBus. The

higher four bits of this register are unused and must be set to

zero. Use of slower conversion times greatly reduces the device

power consumption, as shown in Table VI.

Table VI. Conversion Rate Register Codes

Average Supply Current

Data

Conversion/sec

00h

0.0625

0.17

01h

0.125

0.20

02h

0.25

0.21

03h

0.5

0.24

04h

1

0.29

05h

2

0.40

06h

4

0.61

07h

8

1.1

08h

16

1.9

09h

32

0.73

0Ah

64

1.23

0B to FFh

Reserved

Limit Registers

The ADM1032 has nine Limit Registers to store local and remote,

high, low, and

THERM temperature limits. These registers can

be written to and read back over the SMBus.

The high limit registers perform a > comparison while the low

limit registers perform a < comparison. For example, if the high

limit register is programmed with 80

will result in an alarm condition. If the Low Limit Register is

programmed with 0

°C, measuring 0°C or lower will result in

Alarm condition. Exceeding either the Local or Remote

THERM

limit asserts

THERM low. A default hysteresis value of 10

°C is

provided, which applies to both channels. This hysteresis may

be reprogrammed to any value after power up (Reg 0x21h).

One-Shot Register

The One-Shot Register is used to initiate a single conversion

and comparison cycle when the ADM1032 is in standby mode,

after which the device returns to standby. This is not a data

register as such, and it is the write operation that causes the

one-shot conversion. The data written to this address is irrel-

evant and is not stored. The conversion time on a single shot is

96 ms when the conversion rate is 16 conversions per second or

less. At 32 conversions per second the conversion time is 15.3 ms.

This is because averaging is disabled at the faster conversion rates

(32 and 64 conversions per second).