Datasheet ADT7461 (ON Semiconductor) - 10

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ADT7461 Conversion Rate Register
exceeding either the local or remote high limit asserts The conversion rate register is Address 0x04 at read and THERM2 low. A default hysteresis value of 10°C is Address 0x0A at write. The lowest four bits of this register provided that applies to both THERM channels. This are used to program the conversion rate by dividing the hysteresis value may be reprogrammed to any value after internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, powerup (Register Address 0x21). 512, or 1024 to give conversion times from 15.5 ms (Code It is important to remember that the temperature limits 0x0A) to 16 seconds (Code 0x00). For example, a data format is the same as the temperature measurement data conversion rate of 8 conversions per second means that format. So, if the temperature measurement uses default beginning at 125 ms intervals; the device performs a binary, the temperature limits also use the binary scale. If the conversion on the internal and external temperature temperature measurement scale is switched, however, the channels. temperature limits do not switch automatically. The user This register can be written to and read back over the must reprogram the limit registers to the desired value in the SMBus. The higher four bits of this register are unused and correct data format. For example, if the remote low limit is must be set to 0. The default value of this register is 0x08, set at 10°C and the default binary scale is being used, the giving a rate of 16 conversions per second. Use of slower limit register value should be 0000 1010b. If the scale is conversion times greatly reduces the device power switched to offset binary, the value in the low temperature consumption, as shown in Table 9. limit register should be reprogrammed to be 0100 1010b.
Table 9. CONVERSION RATE REGISTER CODES Status Register Conversion/ Average Supply Current
The status register is a read-only register at Address 0x02.
Code Sec mA Typ at VDD = 5.5 V
It contains status information for the ADT7461. Bit 7 of the status register indicates the ADC is busy 0x00 0.0625 121.33 converting when it is high. The other bits in this register flag 0x01 0.125 128.54 the out-of-limit temperature measurements (Bits 6 to 3 and 0x02 0.25 131.59 Bits 1 to 0) and the remote sensor open circuit (Bit 2). 0x03 0.5 146.15 If Pin 6 is configured as an ALERT output, the following 0x04 1 169.14 applies. If the local temperature measurement exceeds its 0x05 2 233.12 limits, Bit 6 (high limit) or Bit 5 (low limit) of the status 0x06 4 347.42 register asserts to flag this condition. If the remote temperature measurement exceeds its limits, then Bit 4 0x07 8 638.07 (high limit) or Bit 3 (low limit) asserts. Bit 2 asserts to flag 0x08 16 252.44 an open-circuit condition on the remote sensor. These five 0x09 32 417.58 flags are NOR’d together so if any of them is high, the 0x0A 64 816.87 ALERT interrupt latch is set and the ALERT output goes 0x0B to 0xFF Reserved low. Reading the status register clears the five flags, Bits 6 to 2,
Limit Registers
provided the error conditions causing the flags to be set have The ADT7461 has eight limit registers: high, low, and gone away. A flag bit can be reset only if the corresponding THERM temperature limits for both local and remote value register contains an in-limit measurement or if the temperature measurements. The remote temperature high sensor is good. and low limits span two registers each to contain an upper The ALERT interrupt latch is not reset by reading the and lower byte for each limit. There is also a THERM status register. It resets when the ALERT output has been hysteresis register. All limit registers can be written to and serviced by the master reading the device address, provided read back over the SMBus. See Table 13 for address details the error condition has gone away and the status register flag of the limit registers and their power-on default values. bits are reset. When Pin 6 is configured as an ALERT output, the high When Flag 1 and/or Flag 0 are set, the THERM output limit registers perform a > comparison while the low limit goes low to indicate the temperature measurements are registers perform a ≤ comparison. For example, if the high outside the programmed limits. The THERM output does limit register is programmed with 80°C, then measuring not need to be reset, unlike the ALERT output. Once the 81°C results in an out-of-limit condition, setting a flag in the measurements are within the limits, the corresponding status status register. If the low limit register is programmed with register bits are reset automatically and the THERM output 0°C, measuring 0°C or lower results in an out-of-limit goes high. The user may add hysteresis by programming condition. Register 0x21. The THERM output is reset only when the Exceeding either the local or remote THERM limit asserts temperature falls to limit value minus hysteresis value. THERM low. When Pin 6 is configured as THERM2,
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