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ADT7421ARMZ-2RL7 Datasheet(PDF) 9 Page - ON Semiconductor |
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ADT7421ARMZ-2RL7 Datasheet(HTML) 9 Page - ON Semiconductor |
9 / 20 page ADT7421 http://onsemi.com 9 Table 4. Conversion Rate Register Codes Code Conversion/Second Time (Secs) 0x00 0.0625 16 0x01 0.125 8 0x02 0.25 4 0x03 0.5 2 0x04 1 1 0x05 2 500 m 0x06 4 (Default) 250 m 0x07 5 200 m 0x08 10 100 m 0x09 20 50 m 0x0A 36 27 m 0x0B to 0xFF Reserved Limit Registers The ADT7421 has eight limit registers: high, low, and THERM temperature limits for both local and remote temperature measurements. The remote temperature high and low limits span two registers each, to contain an upper and lower byte for each limit. There is also a THERM hysteresis register. All limit registers can be written to, and read back over, the SMBus. See Table 8 for details of the limit register addresses and their power−on default values. When Pin 6 is configured as an ALERT output, the high limit registers perform a > comparison, while the low limit registers perform a ≤ comparison. For example, if the high limit register is programmed with 80 °C, then measuring 81°C results in an out−of−limit condition, setting a flag in the status register. If the low limit register is programmed with 0 °C, measuring 0 °C or lower results in an out−of−limit condition. Exceeding either the local or remote THERM limit asserts THERM low. When Pin 6 is configured as THERM2, exceeding either the local or remote high limit asserts THERM2 low. A default hysteresis value of 10 °C is provided that applies to both THERM channels. This hysteresis value can be reprogrammed to any value after powerup (Register Address 0x21). It is important to remember that the temperature limits data format is the same as the temperature measurement data format. Therefore, if the temperature measurement uses default binary, then the temperature limits also use the binary scale. If the temperature measurement scale is switched, however, the temperature limits do not automatically switch. The user must reprogram the limit registers to the desired value in the correct data format. For example, if the remote low limit is set at 10 °C with the default binary scale, the limit register value is 0000 1010b. If the scale is switched to offset binary, the value in the low temperature limit register needs to be reprogrammed to 0100 1010b. Status Register The status register is a read−only register at Address 0x02. It contains status information for the ADT7421. When Bit 7 of the status register is high, it indicates that the ADC is busy converting. The other bits in this register flag the out−of−limit temperature measurements (Bit 6 to Bit 3, and Bit 1 to Bit 0) and the remote sensor open circuit (Bit 2). If Pin 6 is configured as an ALERT output, the following applies: If the local temperature measurement exceeds its limits, Bit 6 (high limit) or Bit 5 (low limit) of the status register asserts to flag this condition. If the remote temperature measurement exceeds its limits, then Bit 4 (high limit) or Bit 3 (low limit) asserts. Bit 2 asserts to flag an open circuit condition on the remote sensor. These five flags are NOR’ed together, so if any of them is high, the ALERT interrupt latch is set and the ALERT output goes low. Reading the status register clears the five flags, Bit 6 to Bit 2, provided the error conditions causing the flags to be set have gone away. A flag bit can be reset only if the corresponding value register contains an in−limit measurement or if the sensor is good. The ALERT interrupt latch is not reset by reading the status register. It resets when the ALERT output has been serviced by the master reading the device address, provided the error condition has gone away and the status register flag bits are reset. When Flag 1 and/or Flag 0 are set, the THERM output goes low to indicate that the temperature measurements are outside the programmed limits. The THERM output does not need to be reset, unlike the ALERT output. Once the measurements are within the limits, the corresponding status register bits are automatically reset and the THERM output goes high. The user may add hysteresis by programming Register 0x21. The THERM output is reset only when the temperature falls to limit value minus the hysteresis value. When Pin 6 is configured as THERM2, only the high temperature limits are relevant. If Flag 6 and/or Flag 4 are set, the THERM2 output goes low to indicate that the temperature measurements are outside the programmed limits. Flag 5 and Flag 3 have no effect on THERM2. The behavior of THERM2 is otherwise the same as THERM. Table 5. Status Register Bit Assignments Bit Name Function 7 BUSY 1 when ADC Converting 6 LHIGH* 1 when Local High Temperature Limit Tripped 5 LLOW* 1 when Local Low Temperature Limit Tripped 4 RHIGH* 1 when Remote High Temperature Limit Tripped 3 RLOW* 1 when Remote Low Temperature Limit Tripped 2 OPEN* 1 when Remote Sensor Open Circuit 1 RTHRM 1 when Remote THERM Limit Tripped 0 LTHRM 1 when Local THERM Limit Tripped *These flags stay high until the status register is read or they are reset by POR unless Pin 6 is configured as THERM2. Then, only Bit 2 remains high until the status register is read or is reset by POR. |
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