TC654 datasheet(17/38 Pages) MICROCHIP

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DS20001734C-page 17

TC654/TC655

6.0

The TC654/TC655 devices contain 9 registers that pro-

vide a variety of data and functionality control to the

outside system. These registers are listed below in

Table 6-1. Of key importance is the command byte

information, which is needed in the read and write pro-

tocols in order to select the individual registers.

TABLE 6-1:

COMMAND BYTE ASSIGNMENTS

6.1

RPM-OUTPUT1 & RPM-OUTPUT2

Registers (RPM1 & RPM2)

As discussed in Section 4.7 “Sensing Fan Operation

(SENSE1 & SENSE2)”, fan current pulses are detected

at the SENSE1 and SENSE2 inputs of the TC654/

TC655 device. The current pulse information is used to

calculate the fan RPM. The fan RPM data for fans 1 and

2 is then written to registers RPM1 and RPM2, respec-

tively. RPM1 and RPM2 are 9-bit registers that provide

the RPM information in 50 RPM (8-bit) or 25 RPM (9-

bit) increments. This is selected via RES (bit 6<0>) in

the Configuration Register, with ‘0’ = 50 RPM and

‘1’ = 25 RPM. The default state is zero (50 RPM). The

maximum fan RPM value that can be read is

12775 RPM. If this value is exceeded, R2CO (bit 4<0>)

and R1CO (bit 3<0>) in the Status Register will be set to

a '1' to indicate that a counter overflow of the respective

RPM register has occurred. Register 6-1 shows the

RPM output register 9-bit format.

RPM OUTPUT REGISTERS (RPM1 & RPM2)

Command

Read

Write

POR Default State

Function

RPM1

0000 0000

X—

0 0000 0000

RPM Output 1

RPM2

0000 0001

X—

0 0000 0000

RPM Output 2

FAN_FAULT1

0000 0010

0000 1010

Fan Fault 1 Threshold

FAN_FAULT2

0000 0011

0000 1010

Fan Fault 2 Threshold

CONFIG

0000 0100

0000 1010

Configuration

STATUS

0000 0101

X—

00X0 0X00

Status. See Section 6.4 “Status

explanation of X

DUTY_CYCLE

0000 0110

0000 0010

Fan Speed Duty Cycle

MFR_ID

0000 0111

X—

0101 0100

Manufacturer Identification

VER_ID

0000 1000

X—

0000 000X

Version Identification:

(X = ‘0’ TC654, X = ‘1’ TC655)

D(8)

D(7)

D(6)

D(5)

D(4)

D(3)

D(2)

D(1)

D(0)

RPM

0000000000

000000001

000000010

.........

111111110

12750

111111111

12775

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