Page 114 - PDA Robotics Using Your Personal Digital Assistant to Control Your Robot

PDA 05 5/30/03 11:35 AM Page 90
PDA Robotics
This interrupt-on-mismatch feature, together with software config-
urable pull-ups on these four pins, allows easy interface to a keypad
and make it possible for wake-up on key depression.
PORTC and the TRISC Register
PORTC is an 8-bit-wide, bidirectional port. The corresponding data
direction register is TRISC. Setting a TRISC bit (= 1) will make the cor-
responding PORTC pin an input (i.e., put the corresponding output
driver in a Hi-Impedance mode). Clearing a TRISC bit ( 0) will make
the corresponding PORTC pin an output (i.e., put the contents of the
output latch on the selected pin).

PORTC is multiplexed with several peripheral functions. PORTC pins
have Schmitt Trigger input buffers. When the I2C module is enabled,
the PORTC<4:3> pins can be configured with normal I2C levels, or
with SMBus levels by using the CKE bit (SSPSTAT<6>). When enabling
peripheral functions, care should be taken in defining TRIS bits for
each PORTC pin. Some peripherals override the TRIS bit to make a pin
an output, while other peripherals override the TRIS bit to make a pin
an input. Since the TRIS bit override is in effect while the peripheral is
enabled, read modify write instructions (BSF, BCF, XORWF) with
TRISC as destination, should be avoided. The user should refer to the
corresponding peripheral section for the correct TRIS bit settings.

Analog-to-Digital Converter (A/D) Module. The Analog-to-Digital
(A/D) Converter module has five inputs for the 28-pin devices and
eight for the other devices. The analog input charges a sample and
hold capacitor. The output of the sample and hold capacitor is the
input into the converter. The converter then generates a digital result
of this analog level via successive approximation. The A/D conversion
of the analog input signal results in a corresponding 10-bit digital
number. The A/D module has high- and low-voltage reference input
that is software selectable to some combination of VDD, VSS, RA2, or
RA3. The A/D converter has a unique feature of being able to operate
while the device is in SLEEP mode. To operate in SLEEP, the A/D
clock must be derived from the A/D’s internal RC oscillator.
The A/D module has four registers. These registers are:
• A/D Result High Register (ADRESH)

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