Datasheet

PIC16(L)F1782/3
DS41579D-page 126 Preliminary  2011-2012 Microchip Technology Inc.
13.5 PORTB Registers
PORTB is an 8-bit wide, bidirectional port. The
corresponding data direction register is TRISB
(Register 13-11). Setting a TRISB bit (= 1) will make the
corresponding PORTB pin an input (i.e., put the
corresponding output driver in a High-Impedance mode).
Clearing a TRISB bit (= 0) will make the corresponding
PORTB pin an output (i.e., enable the output driver and
put the contents of the output latch on the selected pin).
Example 13-1 shows how to initialize an I/O port.
Reading the PORTB register (Register 13-10) reads the
status of the pins, whereas writing to it will write to the
PORT latch. All write operations are read-modify-write
operations. Therefore, a write to a port implies that the
port pins are read, this value is modified and then written
to the PORT data latch (LATB).
13.5.1 DIRECTION CONTROL
The TRISB register (Register 13-11) controls the PORTB
pin output drivers, even when they are being used as
analog inputs. The user should ensure the bits in the
TRISB register are maintained set when using them as
analog inputs. I/O pins configured as analog inputs
always read ‘0’.
13.5.2 OPEN DRAIN CONTROL
The ODCONB register (Register 13-15) controls the
open-drain feature of the port. Open drain operation is
independently selected for each pin. When an
ODCONB bit is set, the corresponding port output
becomes an open drain driver capable of sinking
current only. When an ODCONB bit is cleared, the
corresponding port output pin is the standard push-pull
drive capable of sourcing and sinking current.
13.5.3 SLEW RATE CONTROL
The SLRCONB register (Register 13-16) controls the
slew rate option for each port pin. Slew rate control is
independently selectable for each port pin. When an
SLRCONB bit is set, the corresponding port pin drive is
slew rate limited. When an SLRCONB bit is cleared,
The corresponding port pin drive slews at the maximum
rate possible.
13.5.4 INPUT THRESHOLD CONTROL
The INLVLB register (Register 13-17) controls the input
voltage threshold for each of the available PORTB
input pins. A selection between the Schmitt Trigger
CMOS or the TTL Compatible thresholds is available.
The input threshold is important in determining the
value of a read of the PORTB register and also the level
at which an interrupt-on-change occurs, if that feature
is enabled. See Section 30.1 “DC Characteristics:
PIC16(L)F1782/3-I/E (Industrial, Extended)” for more
information on threshold levels.
13.5.5 ANALOG CONTROL
The ANSELB register (Register 13-13) is used to
configure the Input mode of an I/O pin to analog.
Setting the appropriate ANSELB bit high will cause all
digital reads on the pin to be read as ‘0’ and allow
analog functions on the pin to operate correctly.
The state of the ANSELB bits has no effect on digital out-
put functions. A pin with TRIS clear and ANSELB set will
still operate as a digital output, but the Input mode will be
analog. This can cause unexpected behavior when
executing read-modify-write instructions on the affected
port.
Note: Changing the input threshold selection
should be performed while all peripheral
modules are disabled. Changing the
threshold level during the time a module is
active may inadvertently generate a tran-
sition associated with an input pin, regard-
less of the actual voltage level on that pin.
Note: The ANSELB bits default to the Analog
mode after Reset. To use any pins as
digital general purpose or peripheral
inputs, the corresponding ANSEL bits
must be initialized to ‘0’ by user software.