LM85 National Semiconductor, LM85 Datasheet - Page 12

• Manufacturer Part Number: LM85
• Description: Hardware Monitor with Integrated Fan Control
• Manufacturer: National Semiconductor

www.national.com
Register
Address
40h
Bit
0
Register
Address
3Fh
Register
Address
3Eh
Functional Description
4.5 Register 3Eh: Company ID
The company ID register contains the company identification number. For National Semiconductor this is 01h. This number is
assigned by Intel and is a method for uniquely identifying the part manufacturer. This register is read only — a write to this
register has no effect.
4.6 Register 3Fh: Version/Stepping
The four least significant bits of the Version/Stepping register [3.0] contain the current stepping of the LM85 silicon. The four most
significant bits [7.4] reflect the LM85 base device number when set to a value of 0110b. All LM85 revisions will have a base
number of 6. For the LM85C, this register will read 01100000b (60h). The LM85B will read 01100010b (62h).If new revisions of
the LM85C or LM85B are released the last 4 bits of this register will change.
The register is used by application software to identify which device in the hardware monitor family of ASICs has been
implemented in the given system. Based on this information, software can determine which registers to read from and write to.
Further, application software may use the current stepping to implement work-arounds for bugs found in a specific silicon
stepping.
This register is read only — a write to this register has no effect.
4.7 Register 40h: Ready/Lock/Start/Override
Name
START
Read/
Write
R/W
Read/
Write
R
Read/
Write
R
Register
Name
Ready/Lock/Start/Override
Register
Name
Version/Stepping
Register
Name
Company ID
R/W
R/W
Default
0
Current Duty
50.196%
100%
(Continued)
Bit 7
(MSB)
7
Bit 7
(MSB)
VER3
.
.
.
.
.
.
Bit 7
(MSB)
RES
Description
When software writes a 1 to this bit, the LM85 fan monitoring and PWM output
control functions will use the values set in the fan control limit and parameter
registers (address 5Ch through 6Eh). Before this bit is set, the LM85 will not
update the used register values, the default values will remain in effect.
Whenever this bit is set to 0, the LM85 fan monitoring and PWM output control
functions use the default fan limits and parameters, regardless of the current
values in the limit and parameter registers (5C through 6Eh). The LM85 will
preserve the values currently stored in the limit and parameter registers when
this bit is set or cleared. This bit becomes read only when the
Ready/Lock/Start/Override register Lock bit is set.
It is expected that all limit and parameter registers will be set by BIOS or
application software prior to setting this bit.
Bit 6
6
Bit 6
VER2
Value (Decimal)
Bit 6
RES
Bit 5
5
128
255
12
Bit 5
VER1
.
.
.
.
.
.
Bit 5
RES
Bit 4
4
Bit 4
VER0
Bit 4
RES
Value (Hex)
Bit 3
3
Bit 3
OVRID
80h
FFh
Bit 3
STP3
.
.
.
.
.
.
Bit 2
2
Bit 2
READY
Bit 2
STP2
Bit 1
1
Bit 1
STP1
Bit 1
LOCK
Bit 0
(LSB)
0
Bit 0
(LSB)
STP0
Bit 0
(LSB)
START
Default
Value
01h
Default
Value
60h
Default
Value
00h