Page 42 - Making PIC Microcontroller Instruments and Controllers

to8Tc 3i

The three registers that conuol PORTB are TRISB, INTCON, and OPTION-REC.
OPIION-REG controls t]le oplional functions of PORTB as follows.

a Bit B0 of OPTION_REG sets prescalar value
I BitBI ofOPTION REG sets prescalar value
r BitB2 of OPTION REG sets prescalar value
r Bit83ofOPTION REG sets the prescalar option (used in low-voltage pogramming)
t Bir B4 of OPTION REG sets Timef0 input pulse edge selection
r Bit B5 ofOPIION REG sets the clock selection
I Bit B6 of OPTION REG sets edge selection for interupts (progranming uses)
: Bit 87 of OPTION-REG sets the pull-ups when cleared (programming uses)

PORTC

PORTC is a full s-bilwide bidirectional poft.
Al1 the pins on PORTC have Schmitt trigger input bulTers. This means they are
designed to be more inrmune to noise on these input lines.
The altemate function of the PORTC pins are defined as fbllows:

r BitC0 VOpinorTimerl Oscillator output or Timerl Clock input
rBitCl VO pin orTimerl Oscillator input or Capture 2 input or Compare 2 output
or Hardware PWM2 output
r BitC2 yO pin or Caprure 1 input or Compare I output or Hardware PwM I output
yO
! Bit C3 pin or Synchronous clock for both SPI and I2C memory modes
r Bit C4 I/O pin or SPI data or data I/O for I2C mode
I Bit C5 VO pin or Synclronous serial port data ouQut
a Bit C6 VO pin or USART Asynchronous transmit ol synchronous clock
r Bit C7 VO pin or USART Asynchronous receive or synchronous data

Special care must be taken when using PORTC'S special function capabilities, in that
some of ttrcse functions will change/set the yO status of certain other pins when in use,
and this can cause unfbreseen complications in the function of other capabilities. See
the datasheet for details.
The rcgister that controls PORTC is the TRISC register. No other registers are
involved. DEFINES are used to set or contlol ce{ain PORTC functions.

Nole The speaker on the IAB-XI board is con ected to pin C I , so the use of this pin
is linited becduse the noise generated by the speaker i)hen this pin is used can be very
iffitating to humans. Since this is one of the lines that allotrs the generatiott of contin'
uous background PWM signals (HPWM 2), it compromises the clean use of this pin
unless the speaker is remo|ed or the siSnal is put thmuqh a gate to clean it up. (l rcc'
ommend that Jou avoid modifcations to the boa l if )ou ca .) The load of the ti )
speaker loacls the pin and can compromise ceftain other uses, but in ost cases you can