AMC6821 Datasheet, PDF (48/54 Pages) Burr-Brown (TI) – Analog Monitor and Control Circuit

AMC6821
SBAS386C – MAY 2006 – REVISED JULY 2007
TACH-DATA Register
Bit 7 (MSB)
TACH-DATA7
TACH-DATA-LByte Register (Address 0x08, Power-On Default = 0x00)
Bit 6
TACH-DATA6
Bit 5
TACH-DATA5
Bit 4
TACH-DATA4
Bit 3
TACH-DATA3
Bit 2
TACH-DATA2
Bit 1
TACH-DATA1
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Bit 0 (LSB)
TACH-DATA0
Bit 7 (MSB)
TACH-DATA15
TACH-DATA-HByte Register (Address 0x09, Power-On Default = 0x00)
Bit 6
TACH-DATA14
Bit 5
TACH-DATA13
Bit 4
TACH-DATA12
Bit 3
TACH-DATA11
Bit 2
TACH-DATA10
Bit 1
TACH-DATA9
Bit 0 (LSB)
TACH-DATA8
Bits [TACH-DATA15:TACH-DATA0] are the number of clock pulses counted during one fan revolution and
represents the period of the fan revolution (refer to the Fan Speed Measurement section). Reading the TACH
data register involves a two-register read. The low byte should be read first. This method causes the high byte to
be frozen until both the high and low byte registers have been read from, preventing erroneous TACH readings.
TACH Setting Register
TACH-SETTING-LByte Register (Address 0x1E, Power-On Default = 0xFF)
Bit 7 (MSB)
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0 (LSB)
TACH-SETTING7 TACH-SETTING6 TACH-SETTING5 TACH-SETTING4 TACH-SETTING3 TACH-SETTING2 TACH-SETTING1 TACH-SETTING0
Bit 7 (MSB)
TACH-
SETTING15
TACH-SETTING-HByte Register (Address 0x1F, Power-On Default = 0xFF)
Bit 6
TACH-
SETTING14
Bit 5
TACH-
SETTING13
Bit 4
TACH-
SETTING12
Bit 3
TACH-
SETTING11
Bit 2
TACH-
SETTING10
Bit 1
TACH-
SETTING9
Bit 0 (LSB)
TACH-
SETTING8
Bits [TACH-SETTING15:TACH-SETTING0] represent the period of the fan revolution (in the number of clock
pulses counted during one revolution), which is equal to the reciprocal of the target fan speed. Refer to the Fan
Speed Measurement section. Software writes this register to set the target RPM in the Software-RPM Control
mode. When the TACH-MODE bit (bit 1, 0x02) is cleared ('0'), the TACH setting must be not greater than the
value corresponding to the RPM for a 30% duty cycle. When the TACH mode is equal to '1', the TACH setting
must be not greater than the value corresponding to the allowed minimum RPM at which the fan properly runs.
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