
- 5 - 
 Andigilog, Inc. 2006 
www.andigilog.com
December
 2006 - 70A05012 
aSC7531A / aSC7531B
Values that would represent temperatures below -273.15°C (0 
K or absolute zero) are reserved and are not be returned 
except as specifically noted. 
For the aSC7531 the required resolution is 0.125°C.   Bits [2:0] 
will be defined but they are beyond the required resolution.  
The sign bit will indicate a negative temperature except when 
reporting an error condition (see 
Sensor Error Condition
).  
Temperature 
80°C 
79.875°C 
1°C 
0°C 
-1°C 
-5°C 
2’s complement representation 
0001  0100  0000  0000 
0001  0011  1111  1000 
0000  0000  0100  0000 
0000  0000  0000  0000 
1111  1111  1100  0000 
1111  1110  1100  0000 
Table 1. Temperature Representation 
Sign 
Integer Temperature 0°C to 512°C 
Fractional 
Temperature 
LSB 0.125°C 
5 
4 
Always Zero 
15 
14 
13 
12 
11 
10 
9 
8 
7 
6 
●
3 
2 
1 
0 
Figure 2. Temperature Reading 
A to D Converter Resolution and Mapping 
The mapping of the A-D converter bit values is a two’s 
complement representation with the binary point between bits 
5 and 6 of the 16-bit data word. Bit 15 is the sign, bits 14 
through 6 are integer temperature in degrees, bits 5 down to 
3 are the fractional part with 0.125°C as the LSB. The lowest 
3 bits are set to zero.  
Temperature Inputs 
The aSC7531A has an internal thermal sensor plus an 
external sensor using a remote diode. The remote sensor is 
calibrated for a 2N3904 NPN transistor that has a non-
ideality (
η
) factor of approximately 1.0046. Use of the remote 
diode is discussed in the Applications Information section. 
The aSC7531B also has an internal thermal sensor plus an 
external sensor using a remote diode however the remote 
sensor is calibrated for an Intel CPU (Pentium 4, 65nM) that 
has a non-ideality (
η
) factor of approximately 1.009. Use of 
the remote diode is discussed in the Applications Information 
section. 
It is recommended that the actual transistor type and 
manufacturers chosen for the remote sensor be 
characterized for non-ideality as part of system qualification. 
Sensor Error Condition 
The aSC7531 has the capability to detect and report open or 
shorted external diode inputs per Sensor Error Condition. 
When an error or failure condition is detected, the sensor 
device must return a large negative value in response to 
either the GetIntTemp() or GetExtTemp() command.  In this 
manner software is provided with a means to determine 
whether or not the sensor is working normally and that the 
data returned is good. 
The aSC7531 will write one of the values from the table 
below to appropriate memory locations for GetIntTemp() 
and/or GetExtTemp().  
The aSC7531 uses the OEM defined values of 0x8102 
(open) and 0x8103 (short) rather than the generic errors 
defined for codes 0x8000 to 0x8003. 
Error Code 
0x8000 to 0x80FF 
Reserved 
0x8102 
Remote Diode Open 
0x8103 
Remote Diode Short 
0x8100-0x81FF 
Reserved 
Description 
Table 2. Error Codes 
Voltage Data 
Accuracy and Resolution 
The aSC7531 measures the following voltages: 
Measured voltages: 
o
12V 
o
5V 
o
3.3V 
o
2.5V 
o
V
CCP
Measurement Error: +/- 2% of full scale 
Resolution: 7.8 mV 
Voltage Data Format 
The data format used to report voltage allows values in the 
range of +/-32V. The voltage sensor data is returned as a 16-
bit 2’s complement binary value.  It represents the number of 
1/1024 volts in the reading if extended the full 16-bits.  This 
allows voltages to be represented with approximately a 1mV 
resolution.