The Microcontroller Idea Book - Jan Axelson's Lakeview Research

Chapter 10
(5) Save the result in the original location (register 9). Bits 5-7 are unchanged from the
original, while bits 0-4 have been changed from 12 (December) to 6 (June).
Listing 10-3 shows how to use the DS1286 in a BASIC-52 system. It’s a long program, but
accomplishes a lot. If you don’t need the alarm or another function, you can shorten the
program by editing out the code for it.
The program begins with a menu that asks you select the desired function: set-up and
initialize, display the time and date, or set the alarm. To initialize the clock/calendar, follow
the prompts in the subroutine beginning at line 200, and enter the information requested.
The program then uses the subroutine at line 3000 to convert the information to BCD, and
stores the result in the appropriate register of the DS1286. When all of the information has
been entered, line 470 starts the clock by bringing bit 7 of register 9 low.
Line 1000 begins the subroutine to display the current time and date. Before reading from
the DS1286, the program clears TE (transfer enable, register B, bit 7). This freezes the
registers at their current values, and allows you to read the complete time and date
information without errors.
If you don’t freeze the registers, if one of them updates in the middle of a series of read
operations, you could end up with an invalid time or date. For example, if you read the hour
just before 10:00, and read the minutes just after 11:00, you will think that it is 10:00 when
it is really 11:00. Freezing the registers ensures that you will read the value of all of the
registers as they were when TE went low. Freezing the registers does not stop the clock,
however. The DS1286 continues to keep track of the time, and when you bring TE high again,
the chip updates the registers to the current time and date.
After the program freezes the registers, it reads the values from the DS1286, uses a
subroutine at line 3100 to convert them from BCD to decimal, and displays the results.
Finally, the program sets TE to update the registers.
A subroutine at line 2000 handles the third function of the program, setting the alarm. To
use this routine, you must wire pin 1 of the DS1286 (INTA) to pin 13 of the 8052-BASIC
(INT1). A menu asks you what type of alarm you would like, prompts you for additional
information, and stores the appropriate values in the DS1286’s registers 3, 5, and 7.
Line 2240 configures INTA as a low-going pulse. An endless loop at lines 2250-2270 then
waits for an interrupt. On interrupt, the program displays the word ALARM and the current
time and date. You could place any program code in the interrupt routine. For example, you
could read sensor data, or write to a port to cause a stepping motor to increment.
180 The Microcontroller Idea Book