Datasheet
2002-2013 Microchip Technology Inc. DS21737B-page 17
TC664/TC665
6.0 REGISTER SET
The TC664/TC665 devices contain 7 registers that pro-
vide a variety of data and functionality control to the
outside system. These registers are listed in Table 6-1.
Of key importance is the command byte information,
which is needed in the read and write protocols to
select the individual registers.
TABLE 6-1: COMMAND BYTE ASSIGNMENTS
6.1 RPM-OUTPUT Register (RPM)
As discussed in Section 4.7, fan current pulses are
detected at the SENSE input of the TC664/TC665
device. The current pulse information is used to calcu-
late the fan RPM. The fan RPM data is then written to
the RPM register. RPM is a 9-bit register that provides
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, RCO (bit 3<0>)
in the Status Register will be set to a '1' to indicate that
a counter overflow of the RPM Register has occurred.
Register 6-1 shows the RPM output register 9-bit for-
mat.
REGISTER 6-1: RPM OUTPUT REGISTER (RPM)
Register Command Read Write POR Default State Function
RPM
0000 0000
X—
0 0000 0000
RPM Output
FAN_FAULT
0000 0010
XX
0000 1010
Fan Fault Threshold
CONFIG
0000 0100
XX
0000 1010
Configuration
STATUS
0000 0101
X—
00X0 0X00
Status. See Section 6.4, Status Reg-
ister explanation of X
DUTY_CYCLE
0000 0110
XX
0000 0010
Fan Speed Duty Cycle
MFR_ID
0000 0111
X—
0101 0100
Manufacturer Identification
VER_ID
0000 1000
X—
0000 00XX
Version Identification:
(XX = ‘10’ TC664, XX = ‘11’ TC665)
D(8) D(7) D(6) D(5) D(4) D(3) D(2) D(1) D(0) RPM
0000000000
00000000125
00000001050
.........
.........
11111111012750
11111111112775