DS14285/DS14287

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RTC ADDRESS MAP

The address map of the DS14285/DS14287 is shown in Figure 2. The address map consists of 114 bytes

of user RAM, 10 bytes of RAM that contain the RTC time, calendar, and alarm data, and 4 bytes which

are used for control and status. All 128 bytes can be directly written or read except for the following:

1. Registers C and D are read-only.

2. Bit 7 of Register A is read-only.

3. The high order bit of the seconds byte is read-only.

The contents of four registers (A,B,C, and D) are described in the “Registers” section.

DS14285/DS14287 ADDRESS MAP Figure 2

TIME, CALENDAR AND ALARM LOCATIONS

The time and calendar information is obtained by reading the appropriate memory bytes. The time,

calendar, and alarm are set or initialized by writing the appropriate RAM bytes. The contents of the 10

time, calendar, and alarm bytes can be either Binary or Binary-Coded Decimal (BCD) format. Before

writing the internal time, calendar, and alarm registers, the SET bit in Register B should be written to a

logic 1 to prevent updates from occurring while access is being attempted. In addition to writing the 10

time, calendar, and alarm registers in a selected format (binary or BCD), the data mode bit (DM) of

Register B must be set to the appropriate logic level. All 10 time, calendar, and alarm bytes must use the

same data mode. The set bit in Register B should be cleared after the data mode bit has been written to

allow the real-time clock to update the time and calendar bytes. Once initialized, the real-time clock

makes all updates in the selected mode. The data mode cannot be changed without reinitializing the 10

data bytes. Table 1 shows the binary and BCD formats of the ten time, calendar, and alarm locations. The

24-12 bit cannot be changed without reinitializing the hour locations.

When the 12-hour format is

selected, the high order bit of the hours byte represents PM when it is a logic one. The time, calendar,