Texas Instruments MSP50C6xx manual Real Time Clock Example, Example 5-1. First Project

C– – Efficiency

5.7.1Real Time Clock Example

The C–– clock works as follows. The Timer2 ISR is set to fire at 1-second intervals. Inside the ISR a counter is incremented by one each time it fires. An assembly routine in cmm1.asm (_getSecondsPassed) disables the interrupts, retrieves the counter, resets it, and turns the interrupts back on. The C–– program calls getSecondsPassed() whenever it is not busy and uses the return value to update the clock. This keeps the assembly code to a minimum and allows all of the calculations to be handled in C––. The interrupts are disabled when the counter is being read to prevent possible loss of time.

_getSecondsPassed

rpt2–2 ; interrupt can still fire for 2 cycles

intd ; leaving these out can cause loss of a second mova0~, *seconds_passed

zaca0

mov*seconds_passed, a0 inte

mova0, a0~ ret

The example is divided up into three projects. The first one is a minimal implementation. It does not have support for speech, LCD, key scanning, or setting the time. It offers minimum functionality to keep the number of files small. It is meant to show the basics of a C–– project.

The second project adds speech and key scanning. The speech provides output and the key scanning is used for input. Adding speech synthesis increases the number of files in the project dramatically, but the C–– is still similar. The main changes that relate to C–– are addition of a routine in cmm1.asm to read buttons on Port D and addition of a routine to speak from C––.

The third project adds LCD support. It offers the same speaking abilities as the third project, but uses an LCD screen for additional output. It also demonstrates the use of arrays in C––.

Example 5–1. First Project

The project is of limited use because there is no way to read the time or change the time without using a scanport. It does provide a good example of a C–– project that contains a few simple files.

A minimum implementation of the real time clock contains the following files.

Code Development Tools 5-39