Page 218 - Making PIC Microcontroller Instruments and Controllers

T|litEBo 215

4 Bit value Prescalar value
0000 1.2
0001 1r4

0010 1:8
0011 l:16
0100 1:32

0101 l:64
0 l l 0 1 : 1 2 8
0111 l:256

applicd ilbjt 3 is set to 1.
lxxx 1:1 No prescalar
Prescalar is therefore OFF
INTCON is the intenupt control regisler

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INTCON 2 BiA Intenupt flag

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INTCON 5 Bits Inteflupt enable bit
INTCON 6 Bit6 Used with Intemrpt enable bit

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As mentioned in the preceding,
there is no way to start and stop Timem. It runs all
the time. Howeve! since it can be written to, it can be set to 0 or any value up to 255
whenever desired. Also in the oounter mode, if there i s no signal on TOCK1 , the counler
will not inclemenq and so no intenupt will occur !hus, in a sense the counter func-
tion (but not the internally clocked timer function) car be stopped. lf running free.
Timer0 genemtes an interrupt every 256 Fosc/4 cycles whether ary attention is paid to
js
the inteffupt or not, so if its interrupt l]ag never cleared, it stays set.
Watchdog timer interaction: If the prcscalar is being used by the watchdog timer,
it cannot be used by Timer2 and visa versa.
Now that we know where all the relevart bits are, we can write a program tbr the
LAB-X1 to testthings out.ln this program, we will sel the prcscalar to its maximum
value to slow things down as far as possible so we can see what is going on more
eas y.