ASC7512 ETC2 [List of Unclassifed Manufacturers], ASC7512 Datasheet - Page 17

• Manufacturer Part Number: ASC7512
• Description: DIGITAL TEMPERATURE SENSOR WITH INTEGRATED FAN CONTROL
• Manufacturer: ETC2 [List of Unclassifed Manufacturers]

Tachometer Measurement and Configuration
Register 28-29h: Fan Tachometer Reading
The Fan Tachometer Reading registers contains the number of 11.111μs periods (90 kHz) between full fan revolutions. The
results are based on the time interval of two tachometer pulses, since most fans produce two tachometer pulses per full
revolution. These registers will be updated at least once every second.
The value, for each fan, is represented by a 16-bit unsigned number.
The Fan Tachometer Reading registers will always return an accurate fan tachometer measurement, even when a fan is
disabled or non-functional, however, if PWM command (register 30h) is zero, tach measurements are suspended and the
last reading may remain in the register.
FF FFh indicates that the fan is not spinning, or that the tachometer input is not connected to a valid signal. These registers
are read-only – a write to these registers has no effect.
When the LSByte of the aSC7512 16-bit register is read, the other byte (MSByte) is latched at the current value until it is
read. At the end of the MSByte read the Fan Tachometer Reading registers are updated. During spin-up, the PWM duty
cycle reported is 0%.
Register 3Ah: Fan Tachometer Measurement Configuration
The Fan Tachometer Configuration registers contain the settings that define the modes of measurement of the Tachometer
input signal. The user is allowed to disable a tachometer measurement or to request PWM stretching, in the case of a 3-wire
fan. Also, the rate, start-up and period of measurements within a fan rotation cycle may be selected. The table below
describes the controls.
© Andigilog, Inc. 2006
Register
Address
Register
Address
28h
29h
3Ah
0:1
5:3
Bit
2
6
7
Read/
Write
Read/
Write
FAN STALLED
R/W
Remote Diode
R
R
Name
Fault
RES
RES
RES
Tach LSB
Tach MSB
Tach1
Configuration
Register Name
Register
Name
R/W
R
R
R
R
R
Disable
(MSB)
Tach1
Bit 7
Default
Table 7 Interrupt Status Register 2
(MSB)
Bit 7
15
0
0
0
0
0
7
Enable
3-Wire
Bit 6
Reserved
The aSC7512 automatically sets this bit to 1 when the TACH1 input reading is
above the count value set in the Tach1 Minimum MSB and LSB registers.
The aSC7512 automatically sets this bit to 1 when there is an open circuit fault
on the Remote1+ or Remote1- thermal diode input pins. A diode fault will also
set bit 4 Diode 1 Zone Limit bit, of Interrupt Status Register 1.
Reserved
Reserved
Bit 6
14
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6
Blank 1
Meas
Bit 5
- 17 -
Bit 5
13
5
Blank 0
Meas
Bit 4
Bit 4
12
4
Dwell 1
Meas
Bit 3
Bit 3
Description
11
3
Dwell 0
Meas
Bit 2
Bit 2
10
2
Duration
Meas
Bit 1
Bit 1
1
August 2006 - 70A05003
1
9
Duration
aSC7512
(LSB)
(LSB)
Meas
Bit 0
Bit 0
0
0
8
Default
Default
Value
Value
N/A
N/A
36