1.0 Functional Description
(Continued)
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.
Remote temperature data is represented by an 11-bit, two’s
complement word with a Least Significant Bit (LSB) equal to
0.125C. 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.
Actual vs. LM64 Remote Temperature Conversion
Actual Remote Diode
Temperature,C
LM64 Remote Diode
Temperature Register, C
Binary Results in LM64
Remote Temperature Register
Hex Remote
Temperature
Register
6800h
6D00h
6E00h
7200h
7700h
7C00h
120
125
126
130
135
140
+104
+109
+110
+114
+119
+124
0110 1000 0000 0000
0110 1101 0000 0000
0110 1110 0000 0000
0111 0010 0010 0000
0111 0111 0000 0000
0111 1100 0000 0000
Output is 11-bit two’s complement word. LSB = 0.125 C.
Actual vs. Remote T_Crit Setpoint Example
Actual Remote Diode
T_Crit Setpoint,C
126
Remote T_CRIT
High Setpoint, C
+110
Binary Remote T_CRIT
High Setpoint Value
0110 1110
Hex Remote T_CRIT
High Setpoint Value
6Eh
Local Temperature data is represented by an 8-bit, two’s
complement byte with an LSB equal to 1C:
Temperature
Digital Output
Binary
0111 1101
0001 1001
0000 0001
0000 0000
1111 1111
1110 0111
1100 1001
Hex
7D
19
01
00
FF
E7
C9
+125C
+25C
+1C
0C
1C
25C
55C
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
DD
as suggested in the table below.
Pin Name
Pin Number
Suggested Pull-up Resistor
Range
1 k
to 2 k
1 k
to 2 k
1 k
to 5 k
1 k
to 5 k
5 k
to 20 k
5 k
to 20 k
5 k
to 20 k
(Note 14)
1 k
to 5 k
Typical
1.5 k
1.5 k
3 k
3 k
10 k
10 k
10 k
(Note 14)
3 k
SMBCLK
SMBDAT
ALERT
T_Crit
A0
GPIOx
GPDx
PWM
TACH
17
16
14
8
12
1-3;18,19
20-24
4
15
Note 14:
Depends on the fan drive circuitry connected to this pin. In the
absence of fan control circuitry use a 1 k
pull-up resistor to V
DD
.
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
, or open:
(1) the Remote Temperature High Byte (RTHB) register is
loaded with 127C, (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 +127C
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 +127C 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 128C (1000 0000) and the OPEN bit in the ALERT
Status Register will not be set. A temperature reading of
128C 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 128C 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.
L
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