TC664 datasheet(20/36 Pages) MICROCHIP

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TC664/TC665

DS21737A-page 20

 2002 Microchip Technology Inc.

6.4

STATUS REGISTER (STATUS)

The Status Register provides all the information about

what is going on within the TC664/TC665 devices. Fan

fault information, VIN status, RPM counter overflow

and over temperature indication are all available in the

Status Register. The Status Register is an 8-bit Read

only register with bits 1, 4, 6 and 7 unused. See

STATUS REGISTER (STATUS)

U-0

R-X

U-0

R-0

R-X

U-X

R-0

—

—OTF

—

RCO

VSTAT

—FF

bit 7

bit 0

bit 7-6

Unimplemented: Read as ‘0’

bit 5

OTF: Over Temperature Fault Condition

For the TC664/TC665 device, this bit is set to the proper state immediately at startup and is

therefore treated as an unknown (X). If VIN is greater than the threshold required for 100% duty

cycle on VOUT (2.6 V typical), then the bit will be set to a ‘1’. If it is less than the threshold, the

bit will be set to ‘0’. This is determined at power-up.

= Over temperature condition has occurred.

= Normal operation, VIN is less than 2.6 V.

bit 4

Unimplemented: Read as ‘0’

bit 3

RCO: RPM Counter Overflow

= Fault condition. The maximum RPM reading of 12775 RPM in register RPM has been

exceeded. This bit will automatically reset to zero when the RPM reading comes back into

range.

= Normal operation. RPM reading is within limits (default).

bit 2

VSTAT: VIN Input Status

For the TC664/TC665 devices, the VIN pin status is checked immediately at power-up. If no

external thermistor or voltage output network is connected (VIN is open), this bit is set to a ‘1’.

If an external network is detected, this bit is set to ‘0’. If the VIN pin is open and SMBus operation

has not been selected in the Configuration Register, the VOUT duty cycle will default to 39.33%.

=VIN is open.

= Normal operation. Voltage present at VIN.

bit 1

Unimplemented: Read as ‘unknown’

bit 0

FF: Fan Fault

= Fault Condition. The value for fan RPM in the RPM Register has fallen below the value set

in the FAN_FAULT Threshold Register. The speed of the fan is too low and a fault condi-

tion is being indicated. The FAULT output will be pulled low at the same time. This fault bit

can be cleared using the Fan Fault Clear bit (FFCLR (bit 7<0>)) in the Configuration Reg-

ister.

= Normal Operation (default).

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit

-n = Value at POR

’1’ = Bit is set

’0’ = Bit is cleared

x = Bit is unknown

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