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DS1744-70IND Datasheet(PDF) 6 Page - Maxim Integrated Products |
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DS1744-70IND Datasheet(HTML) 6 Page - Maxim Integrated Products |
6 / 16 page DS1744/DS1744P Y2K-Compliant, Nonvolatile Timekeeping RAMs 6 of 16 Table 2. Register Map ADDRESS DATA FUNCTION RANGE B7 B6 B5 B4 B3 B2 B1 B0 7FFF 10 Year Year Year 00-99 7FFE X X X 10 Month Month Month 01-12 7FFD X X 10 Date Date Date 01-31 7FFC BF FT X X X Day Day 01-07 7FFB X X 10 Hour Hour Hour 00-23 7FFA X 10 Minutes Minutes Minutes 00-59 7FF9 OSC 10 Seconds Seconds Seconds 00-59 7FF8 W R 10 Century Century Century 00-39 OSC = Stop Bit R = Read Bit FT = Frequency Test W = Write Bit X = See Note BF = Battery Flag Note: All indicated “X” bits are not used but must be set to a “0” during write cycle to ensure proper clock operation. RETRIEVING DATA FROM RAM OR CLOCK The DS1744 is in the read mode whenever OE (output enable) is low, WE (write enable) is high, and CE (chip enable) is low. The device architecture allows ripple-through access to any of the address locations in the NV SRAM. Valid data is available at the DQ pins within tAA after the last address input is stable, providing that the CE and OE access times and states are satisfied. If CE or OE access times and states are not met, valid data is available at the latter of chip-enable access (tCEA) or at output-enable access time (tOEA). The state of the DQ pins is controlled by CE and OE . If the outputs are activated before tAA, the data lines are driven to an intermediate state until tAA. If the address inputs are changed while CE and OE remain valid, output data remains valid for output-data hold time (tOH) but then goes indeterminate until the next address access. WRITING DATA TO RAM OR CLOCK The DS1744 is in the write mode whenever WE and CE are in their active state. The start of a write is referenced to the latter occurring transition of WE or CE . The addresses must be held valid throughout the cycle. CE or WE must return inactive for a minimum of tWR prior to the initiation of another read or write cycle. Data in must be valid tDS prior to the end of write and remain valid for tDH afterward. In a typical application, the OE signal is high during a write cycle. However, OE can be active provided that care is taken with the data bus to avoid bus contention. If OE is low prior to WE transitioning low, the data bus can become active with read data defined by the address inputs. A low transition on WE then disables the output tWEZ after WE goes active. |
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