ASC7521AM8 View Datasheet(PDF) - Unspecified

Part Name

Description

Manufacturer

ASC7521AM8

LOW- OLTAGE 1-WIRE DIGITAL TEMPERATURE SENSOR

Unspecified 

aSC7521A

SST Sensors

The SST temperature sensor provides a means for an analog

signal to travel over a single-wire digital bus enabling remote

temperature sensing in areas previously not monitored in the

PC. The temperature sensor supports an internal temperature

sensor and external thermal diodes.

This section outlines general requirements for Simple Serial

Transport (SST) sensors intended for use in PC desktop

applications that conform to SST Version 1.0 specification.

The aSC7521A reports external temperature sensed by a

remote diode-connected transistor and an internal temperature

measurement.

Addressing

The aSC7521A complies with the address range set aside for

fixed-address, discoverable devices as defined in the SST

Specification Version 1.0. Simple Temperature sensors use

fixed addresses in the range of 0x48 to 0x50. The aSC7521A

may be programmed to any of these addresses via the

address select pins AD0 and AD1.

Device Power-on Timing

Following a power-on reset, such as a system transitioning

from S3-S5 to S0, the aSC7521A will be able to participate in

the address and message timing negotiation and respond to

required SST bus commands such as respond to a GetDIB()

command within 10ms of the device’s VDD rail reaching 90%.

The aSC7521A has an internal power on reset and will be fully

functional within 50ms of power on.

The aSC7521A does not employ any device power

management.

Voltage and Temperature Sensor Data

Little Endian Format

The bit level transfer is defined in the SST specification. The 2-

byte data values are returned in little Endian format, in other

words, the LSB is sent first followed by MSB.

For multi-function devices that allow access to multiple

sensors, the data is returned LSB followed by the MSB for the

first sensor, LSB followed by the MSB for the second sensor,

and so on. The specific order is explicitly specified in the

command description.

Frame Check Sequence (FCS)

Each message requires a frame check sequence byte to

ensure reliable data exchange between host and client. The

message originator and client both make an FCS calculation.

One FCS byte must be returned from the message target to

the originator after all bytes including the header and the data

block are written. If data is read from the target, a second FCS

byte must follow the data block read.

The FCS byte is the result of an 8-bit cyclic redundancy check

(CRC) of the each data block preceding the FCS up to the

most recent, earlier FCS byte. The first FCS in the message

does not include the two address timing negotiation ‘0’ bits that

precede the address byte or the message timing negotiation bit

after the address byte. The first FCS does include the address

byte in its computation. The FCS is initialized at 0x00 and is

calculated in a way that conforms to a CRC-8 represented by

the CRC polynomial, C(x) = x8 + x2 + x + 1.

Bus Voltage

All SST sensor devices used for PC applications must be

capable of operating the SST interface portion of the sensor

device at 1.5 volts as defined in 1.5 Volt Static (DC)

Characteristics section of the SST Version 1.0 specification.

Bus Timing

All SST sensor devices must be able to negotiate timing and

operate at a maximum bus transfer rate of 2-Mbps. If the bus

address timing is negotiated at a lower rate due to the

performance limitations of other devices on the bus, the sensor

device will operate at that lower rate.

Atomic Readings

The aSC7521A ensures that every value returned is derived

from a single analog to digital conversion and is not skewed

(e.g. the MSB and the LSB come from two different

conversions).

Conversion Time

The maximum refresh time for all temperature values is

200ms. The aSC7521A provides the logic to ensure all

readings meet the conversion time requirements.

Temperature Data

Data Precision, Accuracy and Resolution

The temperature data meets the following minimum

requirements:

• Operational Range: -40°C to +125°C

• Internal Sensor Accuracy:

o +/- 3°C over operational range

o +/- 2°C over 40°C to 70°C

• Remote Sensor Accuracy (when TA is from 0°C to

70°C):

o +/- 3°C over operational range

o +/- 1°C over 50°C to 70°C

• Resolution: 0.125°C

Temperature Data Format

The data format is capable of reporting temperature values in

the range of +/-512°C. The temperature sensor data is

returned as a 2’s complement 16-bit binary value. It represents

the number of 1/64°C increments in the actual reading. This

allows temperatures to be represented with approximately a

0.016°C resolution.

© Andigilog, Inc. 2006

-4-

www.andigilog.com

October 2006 - 70A05011

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