Real-Time Clock

Introduction

Each BMX P34 xxxxx processor has a real-time clock which manages:

The current date and time
The date and time of the last application shut-down

When power of the processor is turned off, the real-time clock continues counting during four weeks. This duration is guarantied for a temperature below 45°C (113°F). At a higher temperature this duration is reduced. No maintenance is requested for a real-time clock back up.

Current Date and Time

The processor updates the current date and time in the system words %SW49...%SW53 and %SW70. This data is in BCD (Binary Coded Decimal).

System Word	Most Significant Byte	Least Significant Byte
%SW49	00	Days of the week in the range of values 1 - 7 (1 for Monday and 7 for Sunday)
%SW50	Seconds (0 - 59)	00
%SW51	Hours (0 - 23)	Minutes (0 - 59)
%SW52	Month (1 - 12)	Days of the month (1 - 31)
%SW53	Century (0 - 99)	Year (0 - 99)
%SW70		Week (1 - 52)

Accessing the Date and Time

You can access the date and time as follows:

through the processor debug screen.
with the program:
- Reading system words: %SW49 - %SW53 if the system bit %S50 is at 0,
- immediate update: writing system words %SW50 to %SW53 if the system bit %S50 is at 1,
- incremental update: writing the system word %SW59. With this word the date and time can be set field by field from the current value (if the system bit %S59 is at 1), or an overall increment/decrement can be done.

The following table shows the function performed by each bit in the word %SW59.

Bit Range	Function
0	Increments the day of the week
1	Increments the seconds
2	Increments the minutes
3	Increments the hours
4	Increments the days
5	Increments the months
6	Increments the years
7	Increments the centuries
8	Decrements the day of the week
9	Decrements the seconds
10	Decrements the minutes
11	Decrements the hours
12	Decrements the days
13	Decrements the months
14	Decrements the years
15	Decrements the centuries

NOTE: The function is performed when the corresponding bit %S59 is at 1.

NOTE: The processor does not automatically manage Daylight Savings Time.

Date and Time of the Last Application Shutdown

The date and time of the last application shutdown are in BCD in the system words %SW54 - %SW58.

System Word	Most Significant Byte	Least Significant Byte
%SW54	Seconds (0 to 59)	00
%SW55	Hours (0 to 23)	Minutes (0 to 59)
%SW56	Month (1 to 12)	Days of the month (1 to 31)
%SW57	Century (0 to 99)	Year (0 to 99)
%SW58	Day of the week (1 to 7)	Reason for the last application shutdown

The reason for the last application shutdown can be accessed by reading the least significant byte of the system word %SW58 (value in BCD) which can have the following values.

Word value %SW58	Meaning
1	Application switched to STOP mode.
2	Application stopped by watchdog.
4	Power loss or memory card lock operation.
5	Stop on hardware fault.
6	Stop on software fault (HALT instruction, SFC errors, application CRC check fail, undefined system function call, etc). Details on the software fault type are stored in %SW125.