MAX6650 Maxim, MAX6650 Datasheet - Page 11

• Manufacturer Part Number: MAX6650
• Description: Fan-Speed Regulators and Monitors with SMBus/I2C-Compatible Interface
• Manufacturer: Maxim

Table 5. GPIO Definition Register
Table 6. GPIO Status Register
Alarm Status Register if the condition that caused the
alarm is removed.
The Tachometer Count Registers record the number of
pulses on the corresponding tachometer input during the
period defined by the Tachometer Count-Time Register.
7 (MSB) to 5
7 (MSB)
5 to 4
3 to 2
0 (LSB)
BIT
—
6
BIT
4
3
2
1
(DEFAULT)
GPIO4 (MAX6651 only)
GPIO3 (MAX6651 only)
GPIO2 (MAX6651 only)
STATE
______________________________________________________________________________________
POR
11
11
11
1
1
Always 0
GPIO1
GPIO0
NAME
with SMBus/I
Fan-Speed Regulators and Monitors
(MAX6651
(MAX6651
(MAX6651
GPIO4
GPIO3
GPIO2
GPIO1
GPIO0
only)
only)
only)
PIN
Tachometer
(DEFAULT)
STATE
POR
STATE
0
1
1
1
1
1
00
01
10
11
00
01
10
11
00
01
10
11
0
1
0
1
GPIO4 outputs a logic-level low.
GPIO4 outputs a logic-level high or serves as an input.
GPIO3 outputs a logic-level low.
GPIO3 outputs a logic-level high or serves as an input.
GPIO2 serves as an external clock input.
GPIO2 serves as an internal clock output.
GPIO2 outputs a logic-level low.
GPIO2 outputs a logic-level high or serves as an input.
GPIO1 outputs a logic-level high or serves as an input.
GPIO1 serves as a FULL ON input.
GPIO1 outputs a logic-level low.
GPIO1 outputs a logic-level high or serves as an input.
GPIO0 outputs a logic-level high or serves as an input.
GPIO0 serves as an ALERT output.
GPIO0 outputs a logic-level low.
GPIO0 outputs a logic-level high or serves as an input.
2
C-Compatible Interface
The MAX6651 contains three additional tachometer
inputs, which may be used to monitor additional fans. For
accurate control of multiple fans, use identical fans.
The Tachometer Count-Time Register sets the integration
time over which the MAX6650/MAX6651 count tachome-
ter pulses. The devices can count up to 255 (FFh) pulses
during the selected count time. If more than 255 pulses
occur, the IC sets the overflow alarm and the Tachometer
Count Register reports the maximum value of 255. Set
the time register so the count register will not overflow
under worst-case conditions (maximum fan speed) while
maximizing resolution. Calculate the maximum measur-
able fan speed and minimum resolution with the following
equations:
where t
maximum allowable tachometer input frequency for the
MAX6650/MAX6651.
Max Fan Speed (in RPS) = 255 / (2 x t
Min Resolution (in RPS) = 1 / (2 x t
COUNT
is the tachometer count time; 1kHz is the
FUNCTION
COUNT
COUNT
)
)
11