LM64EVAL National Semiconductor, LM64EVAL Datasheet - Page 12

• Manufacturer Part Number: LM64EVAL
• Description: BOARD EVALUATION LM64
• Manufacturer: National Semiconductor

Specifications of LM64EVAL

• Sensor Type: Temperature, Fan Controller
• Sensing Range: 0°C ~ 85°C
• Interface: SMBus (2-Wire/I²C)
• Sensitivity: ±1°C
• Voltage - Supply: 3 V ~ 3.6 V
• Embedded: Yes, MCU, 8-Bit
• Utilized Ic / Part: LM64
• Lead Free Status / RoHS Status: Not applicable / Not applicable

www.national.com
1.0 Functional Description
1.5 TEMPERATURE DATA FORMAT
Temperature data can only be read from the Local and
Remote Temperature registers. The High, Low and T_CRIT
setpoint registers are Read/Write.
Local Temperature data is represented by an 8-bit, two’s
complement byte with an LSB equal to 1˚C:
1.6 OPEN-DRAIN OUTPUTS, INPUTS, AND PULL-UP
RESISTORS
The SMBDAT, ALERT, T_Crit, GPIO and PWM open-drain
outputs and the GPD, TACH, and A0 inputs are pulled-up by
pull-up resistors to V
Note 14: Depends on the fan drive circuitry connected to this pin. In the
absence of fan control circuitry use a 1 kΩ pull-up resistor to V
Pin Name Pin Number
SMBCLK
SMBDAT
Output is 11-bit two’s complement word. LSB = 0.125 ˚C.
ALERT
Temperature
GPIOx
T_Crit
GPDx
TACH
PWM
A0
Actual Remote Diode
+125˚C
+25˚C
−25˚C
−55˚C
+1˚C
−1˚C
Actual Remote Diode
T_Crit Setpoint,˚C
0˚C
Temperature,˚C
1-3;18,19
126
20-24
120
125
126
130
135
140
17
16
14
12
15
8
4
DD
as suggested in the table below.
0001 1001
0000 0001
0000 0000
1100 1001
0111 1101
1110 0111
1111 1111
Binary
5 kΩ to 20 kΩ
5 kΩ to 20 kΩ
5 kΩ to 20 kΩ
1 kΩ to 2 kΩ
1 kΩ to 2 kΩ
1 kΩ to 5 kΩ
1 kΩ to 5 kΩ
1 kΩ to 5 kΩ
Suggested Pull-up Resistor
(Note 14)
Digital Output
Range
Actual vs. LM64 Remote Temperature Conversion
Temperature Register, ˚C
High Setpoint, ˚C
LM64 Remote Diode
Remote T_CRIT
Actual vs. Remote T_Crit Setpoint Example
+110
(Continued)
(Note 14)
+104
+109
+110
+114
+119
+124
Hex
Typical
1.5 kΩ
1.5 kΩ
10 kΩ
10 kΩ
10 kΩ
7D
FF
E7
C9
19
01
00
3 kΩ
3 kΩ
3 kΩ
DD
.
12
Remote temperature data is represented by an 11-bit, two’s
complement word with a Least Significant Bit (LSB) equal to
0.125˚C. The data format is a left justified 16-bit word avail-
able in two 8-bit registers. Some examples of temperature
conversions are shown below.
1.7 DIODE FAULT DETECTION
The LM64 can detect fault conditions caused by the remote
diode. If the D+ pin is detected to be shorted to V
(1) the Remote Temperature High Byte (RTHB) register is
loaded with 127˚C, (2) the Remote Temperature Low Byte
(RTLB) register is loaded with 0, and (3) the OPEN bit (D2)
in the status register is set. Therefore, if the Remote T_CRIT
setpoint register (RCS): (1) is set to a value less than +127˚C
and (2) the ALERT Mask is disabled, then the ALERT output
pin will be pulled low. If the Remote High Setpoint High Byte
(RHSHB) is set to a value less than +127˚C and (2) the
ALERT Mask is disabled, then the ALERT and T_Crit out-
puts will be pulled low. The OPEN bit by itself will not trigger
an ALERT.
If the D+ pin is shorted to either ground or D−, then the
Remote Temperature High Byte (RTHB) register is loaded
with −128˚C (1000 0000) and the OPEN bit in the ALERT
Status Register will not be set. A temperature reading of
−128˚C indicates that D+ is shorted to either ground or D-. If
the value in the Remote Low Setpoint High Byte (RLSHB)
Register is more than −128˚C and the ALERT Mask is Dis-
abled, ALERT will be pulled low.
1.8 COMMUNICATING WITH THE LM64
Each data register in the LM64 falls into one of four types of
user accessibility:
1. Read Only
2. Write Only
3. Read/Write same address
4. Read/Write different address
A Write to the LM64 is comprised of an address byte and a
command byte. A write to any register requires one data
byte.
Reading the LM64 Registers can take place after the requi-
site register setup sequence takes place. See Section 2.1.1
LM64 Required Initial Fan Control Register Sequence.
Binary Remote T_CRIT
Remote Temperature Register
High Setpoint Value
Binary Results in LM64
0110 1000 0000 0000
0110 1101 0000 0000
0110 1110 0000 0000
0111 0010 0010 0000
0111 1100 0000 0000
0111 0111 0000 0000
0110 1110
Hex Remote T_CRIT
High Setpoint Value
Temperature
Hex Remote
Register
6Eh
6D00h
6E00h
7C00h
6800h
7200h
7700h
DD
, or open: