Datasheet
LM96000
www.ti.com
SNAS234C –APRIL 2004–REVISED MARCH 2013
Table 1. Temperature vs Register Reading (continued)
Temperature Reading (Dec) Reading (Hex)
. . .
. . .
. . .
127°C 127 7Fh
(SENSOR ERROR) 80h
4.3 Register 28-2Fh: Fan Tachometer Reading
Register Read/ Register Bit 7 Bit 0 Default
Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1
Address Write Name (MSB) (LSB) Value
28h R Tach1 7 6 5 4 3 2 LEVEL1 LEVEL0 N/A
29h R LSB 15 14 13 12 11 10 9 8 N/A
Tach1
MSB
2Ah R Tach2 7 6 5 4 3 2 LEVEL1 LEVEL0 N/A
2Bh R LSB 15 14 13 12 11 10 9 8 N/A
Tach2
MSB
2Ch R Tach3 7 6 5 4 3 2 LEVEL1 LEVEL0 N/A
2Dh R LSB 15 14 13 12 11 10 9 8 N/A
Tach3
MSB
2Eh R Tach4 7 6 5 4 3 2 LEVEL1 LEVEL0 N/A
2Fh R LSB 15 14 13 12 11 10 9 8 N/A
Tach4
MSB
The Fan Tachometer Reading registers contain the number of 11.111 µs 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.
The least two significant bits (LEVEL1 and LEVEL2) of the least significant byte are used to indicate the
accuracy level of the tachometer reading. The accuracy ranges from most to least accurate.
[LEVEL1:LEVEL2]=11indicates a most accurate value, [LEVEL1:LEVEL2]=01 indicates the least accurate value
and [LEVEL1:LEVEL2]=00 is reserved for future use.
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 LM96000 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%.
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