Datasheet

MAX6689
register. If extended resolution is desired, the extended
resolution register should be read first. This prevents
the most significant bits from being overwritten by new
conversion results until they have been read. If the
most significant bits have not been read within an
SMBus timeout period (nominally 37ms), normal updat-
ing continues. Table 1 shows the main temperature
register (high-byte) data format, and Table 2 shows the
extended resolution register (low-byte) data format.
Diode Fault Detection
If a channel’s input DXP_ and DXN_ are left open, the
MAX6689 detects a diode fault. An open diode fault does
not cause either ALERT or OVERT to assert. A bit in the
status register for the corresponding channel is set to 1
and the temperature data for the channel is stored as all
1s (FFh). It takes approximately 4ms for the MAX6689 to
detect a diode fault. Once a diode fault is detected, the
MAX6689 goes to the next channel in the conversion
sequence. Depending on operating conditions, a shorted
diode may or may not cause ALERT or OVERT to assert,
so if a channel will not be used, disconnect its DXP and
DXN inputs.
7-Channel Precision Temperature Monitor
8 _______________________________________________________________________________________
Figure 2. SMBus Protocols
TEMP (°C) DIGITAL OUTPUT
> [phone]
[phone]
[phone]
[phone]
0 0000 0000
< 0 0000 0000
Diode fault (open) 1111 1111
Diode fault (short) 1111 1111 or 1110 1110
Table 1. Main Temperature Register
(High-Byte) Data Format
TEMP (°C) DIGITAL OUTPUT
0 000X XXXX
+0.125 001X XXXX
+0.250 010X XXXX
+0.375 011X XXXX
+0.500 100X XXXX
+0.625 101X XXXX
+0.725 110X XXXX
Table 2. Extended Resolution Temperature
Register (Low-Byte) Data Format
S ADDRESS WR ACK ACK PDATA ACKCOMMAND
7 BITS 18 BITS8 BITS
SLAVE ADDRESS: EQUIVA-
LENT TO CHIP-SELECT LINE OF
A 3-WIRE INTERFACE
DATA BYTE: DATA GOES INTO THE REGISTER
SET BY THE COMMAND BYTE (TO SET
THRESHOLDS, CONFIGURATION MASKS, AND
SAMPLING RATE)
WRITE BYTE FORMAT
S ADDRESSADDRESS WR ACK ACK PS RD ACK ///DATACOMMAND
7 BITS 7 BITS 8 BITS8 BITS
READ BYTE FORMAT
SLAVE ADDRESS: EQUIVA-
LENT TO CHIP SELECT LINE
COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
REDING FROM
SPADDRESS WR ACK ACKCOMMAND
7 BITS 8 BITS
SEND BYTE FORMAT
COMMAND BYTE: SENDS COM-
MAND WITH NO DATA, USUALLY
USED FOR ONE-SHOT COMMAND
SPADDRESS RD ACK ///DATA
7 BITS 8 BITS
RECEIVE BYTE FORMAT
DATA BYTE: READS DATA FROM
THE REGISTER COMMANDED
BY THE LAST READ BYTE OR
WRITE BYTE TRANSMISSION;
ALSO USED FOR SMBUS ALERT
RESPONSE RETURN ADDRESS
SLAVE ADDRESS: REPEATED
DUE TO CHANGE IN DATA-
FLOW DIRECTION
DATA BYTE: READS FROM
THE REGISTER SET BY THE
COMMAND BYTE
S = START CONDITION.
P = STOP CONDITION.
SHADED = SLAVE TRANSMISSION.
/// = NOT ACKNOWLEDGED.