Datasheet

ADT7470 Data Sheet
Rev. E | Page 16 of 40
LIMIT AND STATUS REGISTERS
LIMIT VALUES
Associated with each measurement channel on the ADT7470
are high and low limits. These can form the basis of system
status monitoring; a status bit can be set for any out-of-limit
condition and be detected by polling the device. Alternatively,
SMBALERT
interrupts can be generated to automatically flag
a service processor or microcontroller for out-of-limit
conditions as they occur.
TEMPERATURE LIMITS
Table 9 lists the 8-bit temperature limits on the ADT7470.
Table 9. Temperature Limit Registers (8-Bit Limits)
Register Address Description Default
0x44 Temperature 1 Low Limit 0x81
0x45 Temperature 1 High Limit 0x7F
0x46 Temperature 2 Low Limit 0x81
0x47 Temperature 2 High Limit 0x7F
0x48 Temperature 3 Low Limit 0x81
0x49
Temperature 3 High Limit
0x7F
0x4A Temperature 4 Low Limit 0x81
0x4B Temperature 4 High Limit 0x7F
0x4C Temperature 5 Low Limit 0x81
0x4D Temperature 5 High Limit 0x7F
0x4E
Temperature 6 Low Limit
0x81
0x4F
Temperature 6 High Limit
0x7F
0x50 Temperature 7 Low Limit 0x81
0x51 Temperature 7 High Limit 0x7F
0x52 Temperature 8 Low Limit 0x81
0x53 Temperature 8 High Limit 0x7F
0x54 Temperature 9 Low Limit 0x81
0x55 Temperature 9 High Limit 0x7F
0x56 Temperature 10 Low Limit 0x81
0x57 Temperature 10 High Limit 0x7F
FAN SPEED LIMITS
The fan tach measurements are 16-bit results. The fan tach
limits are also 16 bits, consisting of two bytes: a high byte and
low byte. On the ADT7470 it is possible to set both high and
low speed fan limits for over speed and under speed or stall con-
ditions. Be aware that, because the fan tach period is actually
being measured, exceeding the limit by 1 indicates a slow or
stalled fan. Likewise, exceeding the high speed limit by 1
generates an over speed condition.
Table 10. Fan Underspeed Limit Registers
Register Address Description Default
0x58 Tach 1 Min Low Byte 0xFF
0x59
Tach 1 Min High Byte
0xFF
0x5A Tach 2 Min Low Byte 0xFF
0x5B Tach 2 Min High Byte 0xFF
0x5C Tach 3 Min Low Byte 0xFF
0x5D Tach 3 Min High Byte 0xFF
0x5E Tach 4 Min Low Byte 0xFF
0x5F Tach 4 Min High Byte 0xFF
Table 11. Fan Overspeed Limit Registers
Register Address Description Default
0x60 Tach 1 Max Low Byte 0x00
0x61 Tach 1 Max High Byte 0x00
0x62 Tach 2 Max Low Byte 0x00
0x63 Tach 2 Max High Byte 0x00
0x64 Tach 3 Max Low Byte 0x00
0x65 Tach 3 Max High Byte 0x00
0x66 Tach 4 Max Low Byte 0x00
0x67 Tach 4 Max High Byte 0x00
OUT-OF-LIMIT COMPARISONS
Once all limits are programmed, the ADT7470 can be enabled
to begin monitoring. The ADT7470 measures all parameters in
round-robin format and sets the appropriate status bit for out-
of-limit conditions.
Comparisons are done differently depending on whether the
measured value is compared to a high limit or a low limit.
High Limit: > Comparison Performed
Low Limit: ≤ Comparison Performed