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ADM1032 Datasheet(PDF) 7 Page - Analog Devices |
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ADM1032 Datasheet(HTML) 7 Page - Analog Devices |
7 / 12 page REV. 0 ADM1032 –7– Consecutive ALERT Register This value written to this register determines how many out-of- limit measurements must occur before an ALERT is generated. The default value is that one out-of-limit measurement gener- ates an ALERT. The max value that can be chosen is 4. The purpose of this register is to allow the user to perform some filter- ing of the output. This is particularly useful at the faster two conversion rates where no averaging takes place. Table VII. Number of “Out-of-Limit” Register Value Measurements Required yxxx 000x 1 yxxx 001x 2 yxxx 011x 3 yxxx 111x 4 NOTES x = Don’t care bit. y = SMBus timeout bit. Default = 0. See SMBus section for more information. SERIAL BUS INTERFACE Control of the ADM1032 is carried out via the serial bus. The ADM1032 is connected to this bus as a slave device, under the control of a master device. There is a programmable SMBus timeout. When this is enabled the SMBus will timeout after typically 25 ms of no activity. How- ever, this feature is not enabled by default. To enable it, set Bit 7 of the Consecutive Alert Register (Addr = 22h). The ADM1032 supports Packet Error Checking (PEC) and its use is optional. It is triggered by supplying the extra clock for the PEC byte. The PEC byte is calculated using CRC-8. The Frame Check Sequence (FCS) conforms to CRC-8 by the polynomial: C(x) = x8 + x2 + x1 + 1 Consult SMBus 1.1 specification for more information (www.smbus.org). ADDRESSING THE DEVICE In general, every SMBus device has a 7-bit device address (except for some devices that have extended, 10-bit addresses). When the master device sends a device address over the bus, the slave device with that address will respond. The ADM1032 is avail- able with one device address, which is Hex 4C (1001 100). The serial bus protocol operates as follows: 1. The master initiates data transfer by establishing a START condition, defined as a high-to-low transition on the serial data line SDATA, while the serial clock line SCLK remains high. This indicates that an address/data stream will follow. All slave peripherals connected to the serial bus respond to the START condition, and shift in the next eight bits, con- sisting of a 7-bit address (MSB first) plus an R/ W bit, which determines the direction of the data transfer, i.e., whether data will be written to or read from the slave device. The peripheral whose address corresponds to the transmitted address responds by pulling the data line low during the low period before the ninth clock pulse, known as the Acknowl- edge Bit. All other devices on the bus now remain idle while the selected device waits for data to be read from or written Table V. Configuration Register Bit Assignments Power-On Bit Name Function Default 7 MASK1 0 = ALERT Enabled 0 1 = ALERT Masked 6 RUN/STOP 0 = Run 0 1 = Standby 5–0 Reserved 0 Conversion Rate Register The lowest four bits of this register are used to program the conversion rate by dividing the internal oscillator clock by 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, or 1024 to give conversion times from 15.5 ms (code 0Ah) to 16 seconds (code 00h). This register can be written to and read back over the SMBus. The higher four bits of this register are unused and must be set to zero. Use of slower conversion times greatly reduces the device power consumption, as shown in Table VI. Table VI. Conversion Rate Register Codes Average Supply Current Data Conversion/sec mA Typ at VDD = 5.5 V 00h 0.0625 0.17 01h 0.125 0.20 02h 0.25 0.21 03h 0.5 0.24 04h 1 0.29 05h 2 0.40 06h 4 0.61 07h 8 1.1 08h 16 1.9 09h 32 0.73 0Ah 64 1.23 0B to FFh Reserved Limit Registers The ADM1032 has nine Limit Registers to store local and remote, high, low, and THERM temperature limits. These registers can be written to and read back over the SMBus. 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 81oC will result in an alarm condition. If the Low Limit Register is programmed with 0 °C, measuring 0°C or lower will result in Alarm condition. Exceeding either the Local or Remote THERM limit asserts THERM low. A default hysteresis value of 10 °C is provided, which applies to both channels. This hysteresis may be reprogrammed to any value after power up (Reg 0x21h). One-Shot Register The One-Shot Register is used to initiate a single conversion and comparison cycle when the ADM1032 is in standby mode, after which the device returns to standby. This is not a data register as such, and it is the write operation that causes the one-shot conversion. The data written to this address is irrel- evant and is not stored. The conversion time on a single shot is 96 ms when the conversion rate is 16 conversions per second or less. At 32 conversions per second the conversion time is 15.3 ms. This is because averaging is disabled at the faster conversion rates (32 and 64 conversions per second). |
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