SSC050-01 Datasheet, PDF (46/79 Pages) Maxim Integrated Products – Two-Wire Serial Backplane Controller

Control Registers
Control Register Definition
SSC050-01
Data Sheet
39h: Fan Speed Count Overflow 2 (FSCO2)
Register Name:
Address:
Reset Value:
Description
FSCO2
39h
0000_0000b
Fan Speed Count Overflow 2.
This register affects pin P2.6.
7
6
5
4
3
2
1
0
Fan Speed Count Overflow
Bit(s) Bit Label
7 FSCO7-0
Access Description
R/W Fan Speed Count Overflow
These eight bits are compared to the eight-bit fan speed counter. If the counter
exceeds this value, an interrupt will be generated. This register should be loaded
prior to setting the Fan Speed Control Enable (FSCEN) bit in the FSC2 register to
avoid generating unintentional interrupts. The overflow count value can be deter-
mined using the following equation where FF% is equal to the percentage of nominal
RPM which constitutes a fan failure:
Decimal-Overflow-Count-Value = (1,200,000)/(RPM X Divisor X FF%)
Based on the above equation, a divisor of 8 and a detected fan failure at 70% of
nominal RPM, the fan speed monitoring logic is capable of supporting a low end
nominal RPM of 850. High end RPM values are basically unlimited but counter reso-
lution will be diminished above 8000 RPM.
Revision 4.0
November 10, 2004
4-30