DS12887 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 undates in the selected mode the data mode can not be changed without reinitializing the 10 data bytes Table 2 shows the binary and BCD formats of the 10 ti calendar and ala locatio The 24-12bit be teintializing the Whe e 1 ormat of the epres ogic s are alwa s ac they are double nce per se the 10 bytes are 1 by second d chec ed 1 or an alarn 0 dition.Ifa of the time and r data occurs seconds,minutes,hour s,etc.may not correlate. The probability of reading inco orrect time and calen dar data is low.Several methods of avoiding any possible incorrect time and calendar reads are covered later in this text. The three alarm bytes can be used in two ways.First,when the alarm time is written in the appropriate hours,minutes,and seconds alarm locations,the alarm interrupt is initiated at the specified time each day if the alarm enable bit is high.The second use condition is to insert a"don't care"state in one or more of the three alarm bytes.The "don't care"code is any hexadecimal value from Co to FF.The two most significant bits of each byte set the "don't care"condition when at logic 1.An alarm will be generated each hour when the "don't care"bits are set in the hours byte.Similarly,an alarm is generated every minute with"don't care"codes in the hours and minute alarm bytes.The"don't care"codes in all three alarm bytes create an interrupt every second. TIME,CALENDAR AND ALARM DATA MODES Table 2 ADDRESS FUNCTION DECIMAL RANGE LOCATION Range BINARY DATA MODE BCD DATA MODE 0 Seconds 0-59 00-3B 00-59 Seconds Alarm 0.0 00.3B 00.5g Minutes 0.50 00-3B 00.50 0.59 00-3D 00.5 4 1-1 01-0C AM,81-8C PM 01-12AM.81-92P Hours-24-hr Mode 0-23 00-17 00-23 Hours Alarm-12-hr 1-12 01-0CAM.81-8CPM L01-12AM81-92PM Hours Alarm-24-hr 0-23 00-17 00-23 6 Day of the Week 1-7 01-07 01-07 Sunday =1 Date of the Month 121 01-1F 0121 Month 1.12 01-0 01-12 0-99 00-63 00-99 6of19DS12887 6 of 19 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 2 shows the binary and BCD formats of the 10 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 1. The time, calendar, and alarm bytes are always accessible because they are double buffered. Once per second the 10 bytes are advanced by 1 second and checked for an alarm condition. If a read of the time and calendar data occurs during an update, a problem exists where seconds, minutes, hours, etc. may not correlate. The probability of reading incorrect time and calendar data is low. Several methods of avoiding any possible incorrect time and calendar reads are covered later in this text. The three alarm bytes can be used in two ways. First, when the alarm time is written in the appropriate hours, minutes, and seconds alarm locations, the alarm interrupt is initiated at the specified time each day if the alarm enable bit is high. The second use condition is to insert a “don’t care” state in one or more of the three alarm bytes. The “don’t care” code is any hexadecimal value from C0 to FF. The two most significant bits of each byte set the “don’t care” condition when at logic 1. An alarm will be generated each hour when the “don’t care” bits are set in the hours byte. Similarly, an alarm is generated every minute with “don’t care” codes in the hours and minute alarm bytes. The “don’t care” codes in all three alarm bytes create an interrupt every second. TIME, CALENDAR AND ALARM DATA MODES Table 2 ADDRESS RANGE LOCATION FUNCTION DECIMAL RANGE BINARY DATA MODE BCD DATA MODE 0 Seconds 0-59 00-3B 00-59 1 Seconds Alarm 0-59 00-3B 00-59 2 Minutes 0-59 00-3B 00-59 3 Minutes Alarm 0-59 00-3B 00-59 4 Hours-12-hr Mode 1-12 01-0C AM, 81-8C PM 01-12AM, 81-92PM Hours-24-hr Mode 0-23 00-17 00-23 5 Hours Alarm-12-hr 1-12 01-0C AM, 81-8C PM 01-12AM, 81-92PM Hours Alarm-24-hr 0-23 00-17 00-23 6 Day of the Week Sunday = 1 1-7 01-07 01-07 7 Date of the Month 1-31 01-1F 01-31 8 Month 1-12 01-0C 01-12 9 Year 0-99 00-63 00-99