LM93CIMT National Semiconductor, LM93CIMT Datasheet - Page 56

• Manufacturer Part Number: LM93CIMT
• Description: Microprocessor Support IC
• Manufacturer: National Semiconductor

Specifications of LM93CIMT

• Peak Reflow Compatible (260 C): No
• Supply Voltage Max: 3.6V
• Leaded Process Compatible: No
• Supply Voltage Min: 3V
• Operating Temperature Min: 0��C
• Package / Case: 56-TSSOP
• Operating Temperature Max: 85°C
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

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Register
Address
16.0 Registers
16.6.11 Register 6E–75h Fan Tachometer Readings
The 14-bit fan tach readings indicate the number of 22.5 kHz clock periods that occurred during two full periods of the tachometer
input signal. Most fans produce two tachometer pulses per full revolution. These registers must be updated at least once every
second.
The fan tachometer reading registers must always return an accurate fan tachometer measurement, even when a fan is disabled
or non-functional. 3FFFh indicates that the fan is stalled, not spinning fast enough to measure, or the tachometer input is not
connected to a valid signal.
If the pulses per revolution of the fan is known, the RPM can be calculated with the following equation:
RPM= 22500 cycles/sec * 60 sec/min * 2 pulses / COUNT cycles / PULSES_PER_REV
where:
PULSES_PER_REV = the number of pulses that the fan produces per revolution
COUNT
6Eh
6Fh
70h
71h
72h
73h
74h
75h
Read/
Write
R
R
R
R
R
R
R
R
Fan Tach
Fan Tach
Fan Tach
Fan Tach
Fan Tach
Fan Tach
Fan Tach
Fan Tach
Register
Name
MSB
MSB
MSB
MSB
= The 14-bit value read from the tach register
LSB
LSB
LSB
LSB
1
1
2
2
3
3
4
4
(Continued)
Bit 7
Bit 6
Bit 5
TACH2[5:0]
TACH3[5:0]
TACH4[5:0]
TACH[5:0]
56
Bit 4
TACH2[13:6]
TACH3[13:6]
TACH4[13:6]
TACH[13:6]
Bit 3
Bit 2
Bit 1
RES
RES
RES
RES
Bit 0
Default
Value
N/D
N/D
N/D
N/D
N/D
N/D
N/D
N/D