| R.Marek@sh.cvut.cz | 7f15b66 | 2005-05-26 12:42:19 +0000 | [diff] [blame] | 1 | Kernel driver lm77 |
| 2 | ================== |
| 3 | |
| 4 | Supported chips: |
| 5 | * National Semiconductor LM77 |
| 6 | Prefix: 'lm77' |
| 7 | Addresses scanned: I2C 0x48 - 0x4b |
| 8 | Datasheet: Publicly available at the National Semiconductor website |
| 9 | http://www.national.com/ |
| 10 | |
| 11 | Author: Andras BALI <drewie@freemail.hu> |
| 12 | |
| 13 | Description |
| 14 | ----------- |
| 15 | |
| 16 | The LM77 implements one temperature sensor. The temperature |
| 17 | sensor incorporates a band-gap type temperature sensor, |
| 18 | 10-bit ADC, and a digital comparator with user-programmable upper |
| 19 | and lower limit values. |
| 20 | |
| Guenter Roeck | 50bf465 | 2014-04-20 08:07:42 -0700 | [diff] [blame] | 21 | The LM77 implements 3 limits: low (temp1_min), high (temp1_max) and |
| 22 | critical (temp1_crit.) It also implements an hysteresis mechanism which |
| 23 | applies to all 3 limits. The relative difference is stored in a single |
| 24 | register on the chip, which means that the relative difference between |
| 25 | the limit and its hysteresis is always the same for all 3 limits. |
| 26 | |
| 27 | This implementation detail implies the following: |
| 28 | * When setting a limit, its hysteresis will automatically follow, the |
| 29 | difference staying unchanged. For example, if the old critical limit |
| 30 | was 80 degrees C, and the hysteresis was 75 degrees C, and you change |
| 31 | the critical limit to 90 degrees C, then the hysteresis will |
| 32 | automatically change to 85 degrees C. |
| 33 | * All 3 hysteresis can't be set independently. We decided to make |
| 34 | temp1_crit_hyst writable, while temp1_min_hyst and temp1_max_hyst are |
| 35 | read-only. Setting temp1_crit_hyst writes the difference between |
| 36 | temp1_crit_hyst and temp1_crit into the chip, and the same relative |
| 37 | hysteresis applies automatically to the low and high limits. |
| 38 | * The limits should be set before the hysteresis. |