Rainbow Electronics MAX6640 - Manual (Page 13)

• D5: SMBus Timeout Disable. Writing a zero
enables SMBus timeout for prevention of bus lockup.
When the timeout function is enabled, the SMBus
interface is reset if SDA or SCL remains low for more
than 74ms (typ).
• D4: Temperature Channel 2 Source. Selects either
local or remote 2 as the source for temperature
channel 2 register data. Writing a zero to this bit
selects remote 2 for temperature channel 2.
Extended Temperature Registers (05h and 06h)
These registers contain the extended temperature data
from channels 1 and 2. Bits D[7:5] contain the 3 LSBs
of the temperature data. The bit values are 0.5°C,
0.25°C, and 0.125°C. When bit 0 is set to 1, a diode
fault has been detected.
Channel 1 and Channel 2
ALERT
,
OT
, and
THERM
Limits (08h Through 0Dh)
These registers contain the temperatures above which
the ALERT, THERM, and OT status bits set and outputs
assert (for the temperature channels that are not
masked). The data format is the same as that of the
channel 1 and channel 2 temperature registers: the
LSB weight is +1°C and the MSB is +128°C.
Fan 1 and 2 Configuration 1 (10h and 14h)
The following registers control the modes of operation
of the MAX6640:
• D7: PWM Mode. D7 = 1 sets the fan into manual
PWM duty-cycle control mode. Write the target duty
cycle in the fan duty-cycle register. D7 = 0 puts the
fan into RPM control mode. To set RPM manually, set
both fan-control temperature channels (bits D2 and
D3) to zero and write the desired tachometer count
into the TACH count register.
• D[6:4]: Fan Duty-Cycle Rate-of-Change. D[6:4]
sets the time between increments of the duty cycle.
Each increment is 1/120 of the duty cycle. By adjust-
ing the rate of change, audibility of fan-speed
changes can be traded for response time. Table 4
shows the effect of D[6:4] and, for reference, the
time required for the fan speed to change from 33%
to 100% duty cycle as a function of the rate-of-
change bits.
MAX6640
2-Channel Temperature Monitor with Dual
Automatic PWM Fan-Speed Controller
______________________________________________________________________________________ 13
READ/
WRITE
REGISTER
NO.
ADDRESS
POR
STATE
FUNCTION D7 D6 D5 D4 D3 D2 D1 D 0
W 26h
0011
1100 Fan 1 target
duty cycle
MSB — — — — — — LS B
R 27h
0000
0000 Fan 2 current
duty cycle
MSB — — — — — — LS B
W 27h
0011
1100 Fan 2 target
duty cycle
MSB — — — — — — LS B
R/W 28h
0100
000
Channel 1
minimum
fan-start
temperature
MSB — — — — — — LS B
R/W 29h
0100
0000
Channel 2
minimum
fan-start
temperature
MSB — — — — — — LS B
R 3Dh
0101
1000 Read device
ID
0 1 0 1 1 0 0 0
R 3Eh
0100
1101
Read
manufacturer
ID
0 1 0 0 1 1 0 1
R 3Fh
0000
0000 Read device
revision
0 0 0 0 0 0 0 0
Table 3. Register Map (continued)