Page 72 - Making PIC Microcontroller Instruments and Controllers

CONTFOLLING THE OUIFUf AI{D READII{G THE IIIPUT

Using the HPWM (hadware PWM) connnand is abit more compucated in that we must
defiDe certain parameters belbre we can usc thc comnrand. The necessary defines arc

DEFINE CCP1 REG PORTC ; Port to be used by IIPI!'I4 1
DEFINE CCP1 BIT 2 , Pin to be used by HPVil4 1
DEFINE CCP2 REG PORIIC ; Port to be used by HPIiTM 2
DEFINE CCP2 BIT 1 ; Pin !o be used by HPidM 2

You also have to define which timefrhe signal will use so other timers canbc used for
other purposes while the signal is being generated. If a timer is no1 spccjiicd, the
syslem dclaults to Timerl. the 16 bit rimer
The command is
HPt'lM Channel, Dutl,cycle, Flequency

DEFINE.OSC 4
gPm,t 1, 127, 1500 ' qe a, o 6 oJ <q o I d Drl\ a 00 p

creales a 50 pcrccnl duly cycle PWM signal at 1500 Hz (as affected by the definltion
of OSC) on PORTC.2 conlinuously in the background. Also see program 5.9.
The sonmand can be updalcd during runlimc from within a program. As might bc
expected, the pir cannot be used lbr any othcr puryose as long as it is generating the
PWM signal. Turn OFF the PWM mode at lhe CCPconllol rcgister to use the pin as a
normal pin. See the datasheet for mofe infomatior.
The frequencies generated afe limited by the frequency ol thc oscillalor being used
to clock the PIC processo. The minimum freqrency for the PIC 16F877A is 1221 Hz
(with a 20 MHz oscillator). Not all frequencies can be generated. See thc PICBASIC
PRO Compiler manual lbr morc infonnalion on other frequencies.
'l:P.&attim
5;9: Generates a tone on the piezo speaker (There is no looping in ihis
prograrn)
CIJEAR
DEFINE OSC 4
DEFINE CCP1 REG PORTC pori to be used by HP\tl4 1
DEFTNE CCP1 BIT 2 pln !'o De uceo oy Hlwu r
since no riner is denned,
Tinerl vi11 lre used;
HPtill{ !,L27,2500 lhe tone comand
FAUSE 100 pause -1 sec to hear tone
END end proqran to sLop tone-
Next. we will generate sone telephone louchlone loncs on the speaker to demoNtrale
the capability provided by the DTMFOUT command. (Scc Program 5.10.)

DIIMFOVT Pin, {Oms, Offns} ITon€#tTone#,,.}]
Since \\,e will be using Pin C2. ourcommand will look similar !o thc preceding because
rvc are using default vatues for ONms and OFFms