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LM89-1CIMMX Datasheet(PDF) 9 Page - National Semiconductor (TI) |
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LM89-1CIMMX Datasheet(HTML) 9 Page - National Semiconductor (TI) |
9 / 20 page 1.0 Functional Description (Continued) 1. Master Senses SMBus alert line low 2. Master sends a START followed by the Alert Response Address (ARA) with a Read Command. 3. Alerting Device(s) send ACK. 4. Alerting Device(s) send their Address. While transmitting their address, alerting devices sense whether their ad- dress has been transmitted correctly. (The LM89 will reset its ALERT output and set the ALERT mask bit once its complete address has been transmitted successfully.) 5. Master/slave NoACK 6. Master sends STOP 7. Master attends to conditions that caused the ALERT to be triggered. The STATUS REGISTER is read and fan started, setpoint limits adjusted, etc. 8. Master resets the ALERT mask (D7 in the Configuration register). The ARA, 000 1100, is a general call address. No device should ever be assigned this address. Bit D0 (the ALERT configure bit) in the FILTER and ALERT CONFIGURE REGISTER (xBF) must be set low in order for the LM89 to respond to the ARA command. The ALERT output can be disabled by setting the ALERT mask bit, D7, of the Configuration register. The power-on- default is to have the ALERT mask bit and the ALERT configure bit low. 1.3 T_CRIT_A OUTPUT and T_CRIT LIMIT T_CRIT_A is activated when any temperature reading is greater than the limit preset in the critical temperature set- point register (T_CRIT), as shown in Figure 6. The Status Register can be read to determine which event caused the alarm. A bit in the Status Register is set high to indicate which temperature reading exceeded the T_CRIT setpoint temperature and caused the alarm, see Section 2.3. Local and remote temperature diodes are sampled in se- quence by the A/D converter. The T_CRIT_A output and the Status Register flags are updated after every Local and Remote temperature conversion. T_CRT_A follows the state of the comparison, it is reset when the temperature falls below the setpoint RCS-TH. The Status Register flags are reset only after the Status Register is read and if a tempera- ture conversion(s) is/are below the T_CRIT setpoint, as shown in Figure 6. 1.4 POWER-ON-DEFAULT STATES LM89 always powers up to these known default states. The LM89 remains in these states until after the first conversion. 1. Command Register set to 00h 2. Local Temperature set to 0˚C 3. Remote Diode Temperature set to 0˚C until the end of the first conversion. 4. Status Register set to 00h. 5. Configuration register set to 00h; ALERT enabled, Re- mote T_CRIT alarm enabled and Local T_CRIT alarm enabled 6. 85˚C Local T_CRIT temperature setpoint 7. 110˚C Remote T_CRIT temperature setpoint 8. 70˚C Local and Remote HIGH temperature setpoints 9. 0˚C Local and Remote LOW temperature setpoints 10. Filter and Alert Configure Register set to 00h; filter dis- abled, ALERT output set as an SMBus ALERT 11. Conversion Rate Register set to 8h; conversion rate set to 16 conv./sec. 1.5 SMBus INTERFACE The LM89 operates as a slave on the SMBus, so the SMBCLK line is an input and the SMBData line is bi- directional. The LM89 never drives the SMBCLK line and it does not support clock stretching. According to SMBus specifications, the LM89 has a 7-bit slave address. All bits A6 through A0 are internally programmed and can not be changed by software or hardware. The LM89 and LM89-1 versions have the following SMBus slave addresses: Version A6 A5 A4 A3 A2 A1 A0 LM89 1 0 0 1 1 0 0 LM89-1 1 0 0 1 1 0 1 1.6 TEMPERATURE DATA FORMAT Temperature data can only be read from the Local and Remote Temperature registers; the setpoint registers (T_CRIT, LOW, HIGH) are read/write. Remote temperature data is represented by an 11-bit, two’s complement word with an LSB (Least Significant Bit) equal to 0.125˚C. The data format is a left justified 16-bit word 20041529 FIGURE 5. ALERT Output as an SMBus ALERT Temperature Response Diagram 20041506 FIGURE 6. T_CRIT_A Temperature Response Diagram www.national.com 9 |
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