TIMING AND DELAYS
P11

PIC LAB-1 is capable of performing all types of timing and Delay operations. 
Don't let the single external output on the board put you off. You can design programs for one or more outputs and use the 8 LEDs on the board to indicate the state of each output. A new PC board can then be made with relays and driver transistors. 
You should also leave the LEDs on the board to show the state of each output at any particular instant. This is a very clever inclusion as it helps with diagnosis and keeps track of the state of each output.
Timing can start at microseconds and extend to hours, days or months. 
You can have number of random on-off cycles within a program and even include over-riding inputs such as switches and sensors, to vary the timing cycles. 
This section covers a number of experiments, starting with a simple program and advancing to  complex routines with a switch input and a liquid-level sensor (using the "pot" input to detect water conductivity). 
Timing and Delays are the same thing. They all use a DELAY routine. A Delay Routine is a "Do Nothing" routine. It consists of instructions that take time to execute without anything appearing on a display, or anything else happening. 
Before executing a delay, an output can be "set-up" to display a number or value, or a set of LEDs can be illuminated. The delay then allows the eye to view the display, before removing it and displaying another value. 
The same thing can happen to produce a tone. The speaker or piezo is delivered a HIGH and a delay routine is executed. The piezo is then delivered a LOW and a delay routine is called. The action of delivering a HIGH then LOW then HIGH etc will activate the piezo to produce a sound. 
The microcontroller we are using operates at one million instructions per second so the only way to create a program requiring 200,000 instructions, for example, is to create a loop. This is a set of instructions that are executed over and over. Each time they are executed, a file is reduced in value. 
A file contains 256 and this will produce 256 loops. If each loop takes 4 micro-seconds, we have a 1,000 microsecond delay. This is 1 millisecond. 
If this loop is called a number of times by another file, we are already starting to build up a delay of significant duration. 
Delay routines can be designed with loops inside a loop and even three of four loops can be inside other loops. These are called NESTED LOOPS and very soon we have a delay routine that takes minutes, hours and even days to execute. 

EXACT VALUES
One of the challenges is to produce a delay routine that has an exact execution value.  This is needed if you want to produce  accurate timing for a clock etc. 
Since we are using an RC oscillator in the PIC LAB-1, the execution times will not be exact, however it is very easy to increase or decrease their duration to suit an application.  
For exact time intervals, a crystal is needed for the oscillator and this can be the subject for a future experiment. 
Normally, a long delay is not executed by a micro as any push-buttons in the program will not be detected during this time. The answer is to include a button-press feature inside a short delay routine so that they remain operative.   You will see this feature in Expt 20b.

The first experiment produces a beep every minute.  

The time can be altered by approx 0.25sec with each increment or decrement of the value placed in file 1C. This file is the outer file of the nested loop.  Small increments or decrements can be obtained by adjusting the length of the beep. 

TURNING A TIMER ON AND OFF
You can turn the beep on and off by the action of a push button and have the display show "0" for off and "1" for on. 
This involves more programming and the following experiment shows this feature:  

You can increase the time, add two beeps, create a 10 second, 30 second, 10 second, 30 second timer or any number of effects. 

A LONG DELAY
A very long delay can be produced by using Expt20a and calling the 1 minute sub-routine a number of times. The push-button starts the timing and the beep is constant at the end of the timing cycle.
(For demonstration purposes, the time is 2 x 5 seconds). The duration of the beep routine has been shortened so that the start/stop action in Main works instantly. 
For a time-length of 256 x 1 minute, load file 1C in Delay with 0C0h and load file 0Ch in Main with 256.  

TURNING ON 8 OUTPUTS
In this experiment we show how to turn on 8 outputs according to the following chart:
The "ON" times have durations of "2," "4" and "10" seconds.

These could be incorporated into a commercial kitchen, for timing frying of foods or in a production-line. 
It's the universal nature of a microcontroller design that we are covering - the actual type of beep routine is only a concept. We have used low values for counting in the demo experiment below to speed-up the evaluation process.