Datasheet MAX1618 (Maxim) - 9

Remote Temperature Sensor with SMBus Serial Interface MAX1618 Write Byte Format S ADDRESS
WR
ACK COMMAND ACK DATA ACK P
7 bits 8 bits 8 bits Slave Address: equiva- Command Byte: selects which Data Byte: data goes into the register lent to chip-select line of register you are writing to set by the command byte (to set a 3-wire interface thresholds, configuration masks, and sampling rate)
Read Byte Format S ADDRESS
WR
ACK COMMAND ACK S ADDRESS RD ACK DATA
A
P
7 bits 8 bits 7 bits 8 bits Slave Address: equiva- Command Byte: selects Slave Address: repeated Data Byte: reads from lent to chip-select line of which register you are due to change in data- the register set by the a 3-wire interface reading from flow direction command byte
Send Byte Format Receive Byte Format S ADDRESS
WR
ACK DATA ACK P S ADDRESS
WR
ACK DATA
A
P
7 bits 8 bits 7 bits 8 bits Data Byte: writes data to the Data Byte: reads data from register commanded by the the register commanded last Read Byte or Write Byte by the last Read Byte or transmission Write Byte transmission; S = Start condition Shaded = Slave transmission also used for SMBus Alert Response return address P = Stop condition A = Not acknowledged Figure 2. SMBus Protocols and does not go inactive until the temperature drops +3V TO +5.5V below TLOW. +12V Enable thermostat mode through the configuration reg- STBY VCC ister (Table 4), with one bit to enable the feature and another bit to set the output polarity (active high or MAX1618 active low). The ALERT thermostat comparison is made SMBUS after each conversion, or at the end of any SMBus SMBCLK SERIAL transaction. For example, if the limit is changed while INTERFACE the device is in standby mode, the ALERT output (TO HOST) SMBDATA responds correctly according to the last valid A/D DXP result. Upon entering thermostat mode, the ALERT out- put is reset so that if the temperature is in the hysteresis band ALERT initially goes inactive. The power-on reset DXN ALERT (POR) state disables thermostat mode. 2N3904 ADD0
Diode Fault Alarm
A continuity fault detector at DXP detects whether the ADD1 remote diode has an open-circuit condition, short-cir- GND cuit to GND, or short-circuit DXP-to-DXN condition. At the beginning of each conversion, the diode fault is checked, and the status byte is updated. This fault detector is a simple voltage detector; if DXP rises Figure 3. Fan Control Application
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