Datasheet

 2002-2013 Microchip Technology Inc. DS21734B-page 17
TC654/TC655
6.0 REGISTER SET
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, 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 & 2 is then written to registers RPM1 and RPM2,
respectively. 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.
REGISTER 6-1: RPM OUTPUT REGISTERS (RPM1 & RPM2)
Register 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
XX
0000 1010
Fan Fault 1 Threshold
FAN_FAULT2
0000 0011
XX
0000 1010
Fan Fault 2 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 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
00000000125
00000001050
.........
.........
11111111012750
11111111112775