Page 258 - Making PIC Microcontroller Instruments and Controllers

IrI{DEFSTAIDIIIG THE COUITERS: COUilTI G AFEIES

Wretffiffi wiring setup to test the sen-
sitivily ol the phototransistor response.

Special Notes for Timerl Usage

Some of the succeeding paragraphs are fiom the datasheet.

TIMERI OPERATION IiI ASYI{CHROI{OUS COUI{TER IIIODE
The following is what we use for our marble counting exercise.
ff control bit T1S\AnC (TICON<2>) is set, the extemal clbck input is not synchro-
to the intemal phase clocks. The
nized. The timer continues to inuement asyncbrcnous
timer will continue to nm durirg sleep and can generate an interrupt on overflow, which
\ ill wale up lhe processoi Houe\er. \pecial precduuons
in soflware are needed to
reaaywrite the timer (Chapter 6.4. 1 of the datasheet). In asynchronous countet modq
Timerl cannot be used as a time-base for capture or compare opemtions.

READII{G AI{D WRITING TIITIERI II{ ASYI{CHROI{OUS COUI{TER
ll|oDE
Readiry TMR lH or TMR lL while the timer is running liom an extemal asynclfonous
clock will guarartee a valid read (taken care ofin hardware), Howevet the user should