
P
P
- 3 - 
 Andigilog, Inc. 2006 
www.andigilog.com
October 2006 - 70A06010 
aSC7621
Pin Descriptions
Symbol 
Pin 
Type 
Name and Function/Connection 
SMBDAT 
1 
Digital I/O 
(Open-Drain) 
System
Management
Bus
Data.
Open-drain
output.
5V
tolerant, SMBus
2.0
compliant.
S
SMBCLK 
2 
Digital Input 
System Management Bus Clock.  Tied to Open-drain 
output.  5V tolerant, SMBus 2.0 compliant. 
PECI 
7 
Digital I/O 
Platform Environmental Control Interface (PECI).  PECI 1.0 
compliant, CPU digital thermometer input 
P
Vtt 
8 
Analog Input 
PECI reference voltage. 
3.3V 
4 
POWER 
+3.3V pin.  Can be powered by +3.3V Standby power if 
monitoring in low power states is required. This pin should 
be bypassed with a 0.1
μ
F capacitor in parallel with 100pF.  
A bulk capacitance of approximately 10
μ
F needs to be in 
near vicinity of the aSC7621. 
P
GND 
3 
GROUND 
Ground for all analog and digital circuitry. 
5V 
20 
Analog Input 
Analog Input for +5V monitoring. 
12V 
21 
Analog Input 
Analog Input for +12V monitoring. 
2.5V 
22 
Analog Input 
Analog Input for +2.5V monitoring.. 
V
I
VCCP 
23 
Analog Input 
Analog Input for VCCP (processor voltage) monitoring. 
Remote 1+ 
18 
Remote Thermal 
Diode Positive 
Input 
Positive input (current source) from the first remote thermal 
diode Serves as the positive input into the A/D.  Connected 
to THERMDA pin of Pentium processor. 
Remote 1- 
17 
Remote Thermal 
Diode Negative 
Input 
Negative input (current sink) from the first remote thermal 
diode Serves as the negative input into the A/D.  Connected 
to THERMDC pin of Pentium processor. 
Positive input (current source) from the second remote 
thermal diode Serves as the positive input into the A/D.  
Connected to the base of a diode connected MMBT3904 
NPN transistor. 
Negative input (current sink) from the second remote 
thermal diode Serves as the negative input into the A/D.  
Connected to the emitter of a diode connected MMBT3904 
NPN transistor. 
Input for monitoring tachometer output of fan 1.  
Remote 2+ 
16 
Remote Thermal 
Diode Positive 
Output 
R
Remote 2- 
15 
Remote Thermal 
Diode Negative 
Input 
TACH1 
11 
Digital Input 
TACH2 
12 
Digital Input 
Input for monitoring tachometer output of fan 2. 
TACH3 
9 
Digital Input 
Input for monitoring tachometer output of fan 3. During 
power-up, if held low through a 10K
Ω
 resistor, SMBus 
address may be selected based on the state of TACH4 pin. 
F
I
TACH4/AddressSelect 
14 
Digital Input 
Input for monitoring tachometer output of fan 4.  If in 
Address Select Mode, determines the SMBus address of 
aSC7621. 
PWM1/XTESTOUT 
24 
Digital Open-
Drain Output 
Fan speed control 1.  When in XOR tree test mode, 
functions as XOR Tree output. 
PWM2 
10 
Digital Open-
Drain Output 
Fan speed control 2. 
F
PWM3/Address Enable 
13 
Digital Open-
Drain Output 
Fan speed control 3.  Pull to ground at power on to enable 
Address Select Mode (Address Select pin controls SMBus 
address of the device).