Rainbow Electronics MAX6636 - Manual (Page 8)

MAX6636
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 updating con-
tinues. Table 1 shows the main temperature register
(high-byte) data format, and Table 2 shows the extend-
ed resolution register (low-byte) data format. Diode Fault Detection
If a channel’s input DXP_ and DXN_ are left open, the
MAX6636 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 MAX6636 to
detect a diode fault. Once a diode fault is detected, the
MAX6636 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, its DXN and DXP inputs
should be left unconnected.
7-Channel Precision Temperature Monitor
8 _______________________________________________________________________________________
Figure 2. SMBus Protocols
TEMP (°C) DIGITAL OUTPUT
> +127 0111 1111
+127 0111 1111
+126 0111 1110
+25 0001 1001
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
+0.875 111X XXXX
Table 2. Extended Resolution Temperature
Register (Low-Byte) Data Format
S ADDRESS WR ACK ACK P DATA ACK COMMAND
7 BITS 1 8 BITS 8 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 ADDRESS ADDRESS WR ACK ACK P S RD ACK /// DATA COMMAND
7 BITS 7 BITS 8 BITS 8 BITS
READ BYTE FORMAT
SLAVE ADDRESS: EQUIVA-
LENT TO CHIP-SELECT LINE COMMAND BYTE: SELECTS
WHICH REGISTER YOU ARE
REDING FROM
S P ADDRESS WR ACK ACK COMMAND
7 BITS 8 BITS
SEND BYTE FORMAT
COMMAND BYTE: SENDS COM-
MAND WITH NO DATA, USUALLY
USED FOR ONE-SHOT COMMAND
S P ADDRESS 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.