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MIC184BMM Datasheet(PDF) 10 Page - Micrel Semiconductor |
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MIC184BMM Datasheet(HTML) 10 Page - Micrel Semiconductor |
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10 / 21 page  MIC184 Micrel MIC184 10 November 2000 to be read from the MIC184 may then be clocked out. There is one exception to this rule: If the location latched in the pointer register from the last write operation is known to be correct (i.e., points to the desired register), then the “RECEIVE_DATA” procedure may be used. To perform a RECEIVE_DATA, the host sends an address byte to select the slave MIC184, and then retrieves the appropriate number (one or two) of data bytes. Figures 1 through 5 show the formats for these data read and data write procedures. The command byte is 8 bits (1 byte) wide. This byte carries the address of the MIC184 register to be operated upon, and is stored in the MIC184’s pointer register. The pointer register is a write-only register, which is implemented for backward compatibility to the National Semiconductor LM75 and similar devices. The command byte (pointer register) values corre- sponding to the various MIC184 register addresses are shown in Table 2. Command byte values other than 0000 00XX b = 00h through 03h are reserved, and should not be used. The CONFIG register is 8 bits (1 byte) wide. Therefore, communications with the CONFIG register will at a minimum require a READ_BYTE, WRITE_BYTE, or a RECEIVE_BYTE. The TEMP, T_HYST, and T_SET registers are logically nine bits wide. Note, though, that these registers are physically two bytes (one SMBus word) wide within the MIC184. Prop- erly communicating with the MIC184 involves a 16-bit READ_WORD or RECEIVE_WORD from, or WRITE_WORD to, these registers. This is a requirement of the I2C/SMBus serial data protocols, which only allow data transfers to occur in multiples of eight bits. Temperature Data Format The LSB of each 9-bit logical register represents 0.5 °C. The values are in a two’s complement format, wherein the most significant bit (D8) represents the sign: “0” for positive tem- peratures and “1” for negative temperatures. The seven least significant bits of each 16-bit physical register are undefined. Therefore, physical bits D6 through D0 of the data read from these registers must be masked off, and the resulting binary value right justified before using the data received. It is also possible to read only the first byte of any of these three registers, sacrificing 0.5 °C of resolution in exchange for somewhat simpler data handling. However, all writes to the T_SET and T_HYST registers must be in the 16-bit WRITE_WORD format. Table 3 shows examples of the data format used by the MIC184 for temperatures. A/D Converter Timing Whenever the MIC184 is not in its low power shutdown mode, the internal A/D converter (ADC) attempts to make continu- ous conversions unless interrupted by a bus transaction accessing the MIC184. When the MIC184 is accessed, the conversion in progress will be halted, and the partial result discarded. When the access of the MIC184 is complete the ADC will begin a new conversion cycle, with results valid t CONV after that. Figure 6 shows this behavior. tCONV is twice as long for external conversions as it is for internal conver- sions. This allows the use of a filter capacitor on the A2/T1 input without a loss of accuracy due to the resulting longer settling times. Power-On When power is initially applied, the MIC184’s internal regis- ters are set to default states which make the MIC184 com- pletely backward compatible with the LM75. Also at this time, the levels on the address inputs A2, A1, and A0 are read to establish the device’s slave address. The MIC184’s power- up default state can be summarized as follows: • Normal-mode operation (MIC184 not in shutdown) • ZONE is set to internal (on-chip temperature sensing) • INT function is set to comparator mode • INT output is set to active-low operation • Fault_Queue depth = 1 • Interrupts are enabled (IM = 0) • T_SET = +80 °C; T_HYST = +75°C In order to accommodate the use of A2/T1 as a dual-purpose input, there is a weak pulldown on A2/T1 that will attempt to sink ≈25µA from the pin to ground for t POR following power- up of the MIC184. This allows the MIC184 to pull A2/T1 to a low state when a diode junction is connected from that pin to ground, and latch a zero as the A2 address value. If A2 is not to be used as a diode connection, it should be connected to V DD or ground. Note that a fault in the external temperature sensor (if used) may not be reported until one or more conversion cycles have been completed following power-on. See DIODE FAULTS. e r u t a r e p m e Ty r a n i B w a Ry r a n i B d e k s a Mx e H d e k s a M C ° 5 2 1 +X X X X X X X 0 1 0 1 1 1 1 1 00 1 0 1 1 1 1 1 0 b A F 0 h C ° 5 2 +X X X X X X X 0 1 0 0 1 1 0 0 00 1 0 0 1 1 0 0 0 b 2 3 0 h C ° 5 . 0 +X X X X X X X 1 0 0 0 0 0 0 0 01 0 0 0 0 0 0 0 0 b 1 0 0 h C ° 0X X X X X X X 0 0 0 0 0 0 0 0 00 0 0 0 0 0 0 0 0 b 0 0 0 h C ° 5 . 0 – X X X X X X X 1 1 1 1 1 1 1 1 11 1 1 1 1 1 1 1 1 b F F 1 h C ° 5 2 – X X X X X X X 0 1 1 1 0 0 1 1 10 1 1 1 0 0 1 1 1 b E C 1 h C ° 0 4 – X X X X X X X 0 0 0 0 1 1 0 1 10 0 0 0 1 1 0 1 1 b 0 B 1 h C ° 5 5 – X X X X X X X 0 1 0 0 1 0 0 1 10 1 0 0 1 0 0 1 1 b 2 9 1 h Table 3. Digital Temperature Format |
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