Rainbow Electronics LM63 - Manual (Page 10)

1.0 Functional Description
(Continued)
1.3 SMBus INTERFACE
Since the LM63 operates as a slave on the SMBus the
SMBCLK line is an input and the SMBDAT line is bi-
directional. The LM63 never drives the SMBCLK line and it
does not support clock stretching. According to SMBus
specifications, the LM63 has a 7-bit slave address. All bits,
A6 through A0, are internally programmed and cannot be
changed by software or hardware.
The complete slave address is:
A6 A5 A4 A3 A2 A1 A0
1 0 0 1 1 0 0
1.4 POWER-ON RESET (POR) DEFAULT STATES
For information on the POR default states see Section 2.2
LM63 Register Map in Functional Order.
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
0.125˚C. The data format is a left justified 16-bit word avail-
able in two 8-bit registers:
Temperature
Digital Output
Binary Hex
+125˚C 0111 1101 0000 0000 7D00
+25˚C 0001 1001 0000 0000 1900
+1˚C 0000 0001 0000 0000 0100
+0.125˚C 0000 0000 0010 0000 0020
0˚C 0000 0000 0000 0000 0000
−0.125˚C 1111 1111 1110 0000 FFE0
−1˚C 1111 1111 0000 0000 FF00
−25˚C 1110 0111 0000 0000 E700
−55˚C 1100 1001 0000 0000 C900
Local Temperature data is represented by an 8-bit, two’s
complement byte with an LSB equal to 1˚C:
Temperature
Digital Output
Binary Hex
+125˚C 0111 1101 7D
+25˚C 0001 1001 19
+1˚C 0000 0001 01
0˚C 0000 0000 00
−1˚C 1111 1111 FF
−25˚C 1110 0111 E7
−55˚C 1100 1001 C9
1.6 OPEN-DRAIN OUTPUTS
The SMBDAT, ALERT, and PWM outputs are open-drain
outputs and do not have internal pull-ups. A “High” level will
not be observed on these pins until pull-up current is pro-
vided by an internal source, typically through a pull-up resis-
tor. Choice of resistor value depends on several factors but,
in general, the value should be as high as possible consis-
tent with reliable operation. This will lower the power dissi-
pation of the LM63 and avoid temperature errors caused by
self-heating of the device. The maximum value of the pull-up
resistor to provide the 2.1 V high level is 88.7 k
Ω.
1.7 DIODE FAULT DETECTION
The LM63 can detect fault conditions caused by the remote
diode. If the D+ pin is detected to be shorted to V
DD
, or open:
(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 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 LM63
Each data register in the LM63 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 LM63 is comprised of an address byte and a
command byte. A write to any register requires one data
byte.
Reading the LM63 Registers can take place after the requi-
site register setup sequence takes place. See Section 2.1.1
LM63 Required Initial Fan Control Register Sequence.
The data byte has the Most Significant Bit (MSB) first. At the
end of a read, the LM63 can accept either Acknowledge or
20057009
FIGURE 5. ALERT Output as an SMBus ALERT
Temperature Response Diagram
LM63
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