Page 60 - Making PIC Microcontroller Instruments and Controllers

q6 .r'N-rROLLlxG THE OUTPU-I AND NEADIiIG THE INPUT

ln general, the ports on the microcontrollers (MCUS) are designed so they can be used
as inputs or as outputs, In fact, the ports can be programmed so celtain pins on a po
are inputs and others are outputs. All we have to do is lell the program what we want
done and the compiler will handle the details. The compiler not only allows you to define
how you will use the pins of each port, it can also set them up as inputs or as outputs
automatically, depending on the instructions you use to address the pin in your program.
You have a choice of setting PORTD to an output port and then setting pin I on this
ponhigh, or you can simplytell the compilerto make pin 1 of PORTD high and it will
take care of the setting up details.
The ports can be treatcd just like any other memory location in the microcontroller'
By name, you can read them, setthem, aLnd use them in calculations and manipulatlons
just like you canwith any other named orunnamedmemory location.lfthings are con_
nected to the po s and pins, ihe program will interact with, and respond 1o, whatever
is connected to them. (Any named port, register, or pin can be addressed directly by name
for all purposes when using the PBP Compiler They are called out as they are named
in the datasheet for each individual PIC by lhe manufacturer)

Blink One LED

Type the following program (Prognm5.1) into yourPC and save it lt does notneecl
to be saved in the same directory as t}Ie PBPexe program. To keep with the con-
ventions being used in the compiler manual, call this program myBLINK.BAS so it
does not overwrite the BLINK.BAS program provided on the disk thal came with
the LAB Xl.
The program to control pin 0 of PORTD is as fbllows:

lliP$iim$lll controlling (blinking) an LED (Blinking an LED [We are usins lhe
rightmost LED on the bargraphl)

CLEJAR clear nenory LocaLions
DEFINE OgC {
nooP:
HIGE PORTD. O lurns LED connecled Lo D0 oN
PAUSE 500 deLay 0.5 seconds
IJO!' PORTD. O turns LED connecled to D0 oFF
PAUSE 500 delay 0.5 seconds
GOIO LOOP qro back to Loop and repeat operation
END aL1 prograns nust end with END

The program demonstrates the most elementary control we have over an output: that
of turning it ON and OFF In this program, we did not have to set the port directions
(with the TRIS conmand), because the HIGH and Low command tale care of that aulo
matically. (If we used PORTD.0=I instead ol HIGH PORTD.0, we would have had to