Datasheet ADT7461A (ON Semiconductor) - 10

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ADT7461A Table 9. CONFIGURATION REGISTER BIT
and lower byte for each limit. There is also a THERM
ASSIGNMENTS
hysteresis register. All limit registers can be written to, and read back over, the SMBus. See Table 14 for details of the
Power-On
limit register addresses and their power-on default values.
Bit Name Function Default
When Pin 6 is configured as an ALERT output, the high 7 MASK1 0 = ALERT Enabled 0 limit registers perform a > comparison, while the low limit 1 = ALERT Masked registers perform a ≤ comparison. For example, if the high 6 RUN/STOP 0 = Run 0 limit register is programmed with 80 1 = Standby °C, then measuring 81°C results in an out-of-limit condition, setting a flag in the 5 ALERT/ 0 = ALERT 0 THERM2 1 = THERM2 status register. If the low limit register is programmed with 0°C, measuring 0°C or lower results in an out-of-limit 4, 3 Reserved 0 condition. 2 Temperature 0 = 0°C to 127°C 0 Exceeding either the local or remote THERM limit asserts Range Select 1 = Extended Range THERM low. When Pin 6 is configured as THERM2, 1, 0 Reserved 0 exceeding either the local or remote high limit asserts THERM2 low. A default hysteresis value of 10
Conversion Rate Register
°C is The conversion rate register is Address 0x04 at read and provided that applies to both THERM channels. This Address 0x0A at write. The lowest four bits of this register hysteresis value can be reprogrammed to any value after are used to program the conversion rate by dividing the powerup (Register Address 0x21). internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, It is important to remember that the temperature limits 512, or 1024 to give conversion times from 15.5 ms data format is the same as the temperature measurement data (Code 0x0A) to 16 seconds (Code 0x00). For example, a format. Therefore, if the temperature measurement uses conversion rate of eight conversions per second means that default binary, then the temperature limits also use the beginning at 125 ms intervals, the device performs a binary scale. If the temperature measurement scale is conversion on the internal and the external temperature switched, however, the temperature limits do not channels. automatically switch. The user must reprogram the limit The conversion rate register can be written to and read registers to the desired value in the correct data format. For back over the SMBus. The higher four bits of this register are example, if the remote low limit is set at 10°C with the unused and must be set to 0. The default value of this register default binary scale, the limit register value is 0000 1010b. is 0x08, giving a rate of 16 conversions per second. Use of If the scale is switched to offset binary, the value in the low slower conversion times greatly reduces the device power temperature limit register needs to be reprogrammed to consumption. 0100 1010b.
Status Register Table 10. CONVERSION RATE REGISTER CODES
The status register is a read-only register at Address 0x02.
Conversion/
It contains status information for the ADT7461A.
Code Second Time (Seconds)
When Bit 7 of the status register is high, it indicates that the 0x00 0.0625 16 ADC is busy converting. The other bits in this register flag the 0x01 0.125 8 out-of-limit temperature measurements (Bit 6 to Bit 3, and 0x02 0.25 4 Bit 1 to Bit 0) and the remote sensor open circuit (Bit 2). If Pin 6 is configured as an ALERT output, the following 0x03 0.5 2 applies: If the local temperature measurement exceeds its 0x04 1 1 limits, Bit 6 (high limit) or Bit 5 (low limit) of the status 0x05 2 500 m register asserts to flag this condition. If the remote 0x06 4 250 m temperature measurement exceeds its limits, then Bit 4 0x07 8 125 m (high limit) or Bit 3 (low limit) asserts. Bit 2 asserts to flag 0x08 16 62.5 m an open circuit condition on the remote sensor. These five 0x09 32 31.25 m flags are NOR’ed together, so if any of them is high, the 0x0A 64 15.5 m ALERT interrupt latch is set and the ALERT output goes low. 0x0B to 0xFF Reserved Reading the status register clears the five flags, Bit 6 to
Limit Registers
Bit 2, provided the error conditions causing the flags to be The ADT7461A has eight limit registers: high, low, and set have gone away. A flag bit can be reset only if the THERM temperature limits for both local and remote corresponding value register contains an in-limit temperature measurements. The remote temperature high measurement or if the sensor is good. and low limits span two registers each, to contain an upper
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