Page 252 - Making PIC Microcontroller Instruments and Controllers

2so UIDERST NoI G tHE COUIIERS: COUNII|{G MARBLES

signal because an intenupt can only be se! once. The intenupt routine toggles pin B.4
up and down, and since pinB.4 is connected topin C.0, the signal is fed to C.0. We are
using pin C.0 because it is the only pin thal can be used as an input for the Timer I reg-
ister pair as indicatcd in the data sheet.
IHE WORKING PROGRAIU
Program 17.5 demonstmtes fundamental TMR I operation as a counlcr lor the marbles. As writ
ten it counls the nunbcr of lines PORTB.0 is grounded- Displays show Lrs the following things

i
' t \ t . O \ 6 g s r o s e a . o d d p o L s - . - I j o r " r r ' o
B register (too fast to see, add pauses if you ranr
TMR1L and TMR1H registers

ltorking connections are
Connect 81 to C0 to feed Tinerl counter
Gromd B0 Lo increment the counter.
in Program 17.5.
The above ideas are implemented

riatiii!!iiii:!l?!!l:i Basic marble countins routineio count directlyto theTimerl
counter register pair (The wiring diagram lhis program n Fig!re 17-5)
lor
is
cL&dR ; always start riLh c1ear. Good habit.
DEFINE osc 4 ; -la o p..d. (ood holr'
DEFINE ICD DREG PORTD ; de6ne LCD connectioNs dAtA PORTB
DEFINE LCD DBIT 4 i 4 brt path
DEFrtitE LCD_RSREG PORTE ; register Select port
DEFrrlE rJcD_RsBtt 0 ; regisler select biL
DEFIAIE I,CD EREG PORTE , enable poTI
DEFINE tCD EBIIr L ; enable bit
LOW POR1[E.2 ; sel low to write only
DEFINE LCD-COM!4aI'IDUS 2000 ; deLay in nicro seconds
DEFINE I,CD_DATAUS 50 ; delay in nicro seconds
.a.DcoN1-%00000111 ; set ADcoNl for diqilal operation

IRIsA=%00000000
TRISB=%11110001
TRISC=%00001111
TRISE=%00000000
X VAR WORD

!E1CON=%o000 0011 ; set bils to conLrol time.1. Pae'e 56
; bitT=o Not used
; biL6=0 Not ,rsed
; bit5=0 Prescalar=1
; bi!4=0 PrescaLar=
; bir3=0 osc enable bi!. osc off