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LM81 Datasheet(PDF) 23 Page - National Semiconductor (TI) |
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LM81 Datasheet(HTML) 23 Page - National Semiconductor (TI) |
23 / 33 page Functional Description (Continued) masks for each Interrupt. As described in Section 3.3, the hardware Interrupt line can also be enabled/disabled in the Configuration Register. T_CRIT_A interrupt is dedicated to temperature and is indi- cated in Extended Mode Register 1. Extended Mode Regis- ter 1 controls T_CRIT_A. 9.1 Interrupt Clearing Reading a Status Register will output the contents of the Register, and reset the Register. A subsequent read done before the analog “round-robin” monitoring loop is complete will indicate a cleared Register. Allow at least 820 ms to allow all Registers to be updated between reads. In summary, the Interrupt Status Register clears upon being read, and re- quires at least 400 ms to be updated. When the Interrupt Status Register clears, the hardware interrupt line will also clear until the Registers are updated by the monitoring loop. The hardware Interrupt line (INT) is cleared with the INT_Clear bit, which is Bit 3 of the Configuration Register. When this bit is high, the LM81 monitoring loop will stop. It will resume when the bit is low. 10.0 RESET I/O RESET is intended to provide a master reset to devices connected to this line. INT Mask Register 2, Bit 7, must be set high to enable this function. Setting Bit 4 in the Configu- ration Register high outputs a least 20 ms low on this line, at the end of which Bit 4 in the Configuration Register automati- cally clears. Again, the label for this pin is only its suggested use. In applications where the RESET capability is not needed it can be used for any type of digital control that requires a 20 ms active low open-drain output. RESET operates as an input when not activated by the Configuration Register. Setting this line low will reset all of the registers in the LM81 to their power on default state. All Value RAM locations will not be affected except for the DAC Data Register. 11.0 NAND TREE TESTS A NAND tree is provided in the LM81 for Automated Test Equipment (ATE) board level connectivity testing. DACOut/ NTEST_IN, T_CRIT_A, V + and GND pins are excluded from NAND tree testing. Taking DACOut/NTEST_IN high before the first write to the configuration register activates the NAND Tree test mode. After the first write to the configura- tion register the NAND Tree test mode cannot be reacti- vated. To perform a NAND tree test all pins included in the NAND tree should be driven to 1 forcing the A0/ NTEST_OUT high. Each individual pin starting with A1 and concluding with SMBData (excluding DACOut/NTEST_IN, T_CRIT_A, V + and GND) can be taken low with the resulting toggle observed on the A0/NTEST_OUT pin. Allow for a typical propagation delay of 500 ns. DS100072-29 www.national.com 23 |
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