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PC87306 Datasheet(PDF) 87 Page - National Semiconductor (TI) |
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PC87306 Datasheet(HTML) 87 Page - National Semiconductor (TI) |
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87 / 110 page  100 Keyboard Controller and Real-Time Clock (Continued) TABLE 10-2 RTC Memory Map Index Function BCD Format Binary Format Comments (RAMSEL e 0) 00 Seconds 00 – 59 00 – 3b RW 01 Seconds Alarm 00 – 59 00 – 3b RW 02 Minutes 00 – 59 00 – 3b RW 03 Minutes Alarm 00 – 59 00 – 3b RW 04 Hours 12 hr e 01 – 12 (AM) 01 – 0c (AM) RW 12 hr e 81 – 92 (PM) 81 – 8c (PM) RW 24 hr e 00–23 00–17 R W 05 Hours Alarm 12 hr e 01 – 12 (AM) 01 – 0c (AM) RW 12 hr e 81 – 92 (PM) 81 – 8c (PM) RW 24 hr e 00–23 00–17 R W 06 Day of Week 01 – 07 01 – 07 (Sunday e 1) RW 07 Date of Month 01 – 31 01 – 1f RW 08 Month 01–12 01 – 0c RW 09 Year 00 – 99 00 – 63 RW 0A Control Register A RW (Bit 7 is Read Only) 0B Control Register B RW (Bit 3 is Read Only) 0C Control Register C R 0D Control Register D R 0E – 7F Battery-Backed RAM RW (114 Bytes) (RAMSEL e 1) 00 – 7F Battery-Backed RAM RW (128 Bytes) Rext e 5kX C1 e 12 x 15 pF C2 e 15 pF Cparasitic e 0 x 8pF TLC12379 – 96 FIGURE 10-13 Oscillator Internal and External Circuitry The start-up time of this oscillator may vary from two to seven seconds and is due to the high ‘‘Q’’ of the crystal The parameters below describe the crystal to be used Parallel Resonant tuning fork (N cut) or XY Bar Q l 35k Load Capacitance (CL) 9 pF to 13 pF Accuracy User Choice Temperature Coefficient User Choice 1024 Time Keeping The time is kept in BCD or binary format The format is determined by bit 2 of Control Register B (DM) Either 12 or 24 hour representation for the hours can be maintained as determined by bit 1 of Control Register B (2412) Note that when changing the format the time registers must be re-ini- tialized to the corresponding data format Daylight savings and leap year exceptions are handled by the time keeping function When bit 0 of Control Register A (DSE) is a ‘‘1’’ time advances from 15959 AM to 30000 on the first Sunday in April On the last Sunday of October time changes from 15959 to 10000 when daylight savings is enabled On leap year February is extended to 29 days The time is updated once per second If a read of the timing registers coincides with an update data read may not be valid Also writes to time registers during an update have undefined results To avoid accessing invalid data the RTC in the PC87306 provides a user copy of the time registers The sequence used to update the time registers is shown in Figure 10-14 Four methods are available for reading and writing time to ensure that the correct time is written or read They are as follows Method 1 Set the SET bit (CRB7) Set the SET bit to 1 This takes a snapshot of the internal time registers and loads it into the user copy Then when the SET bit is written with 0 the user copy will update the internal registers Method 2 Access after detection of an Update Ended Interrupt This interrupt indicates that an update has just completed and the next update will occur after 999 ms Method 3 Poll update-in-progress (bit 7 in Control Reg- ister A) 87 |
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