Microchip Technology MA330025-1 Data Sheet

 2009-2012 Microchip Technology Inc.

DS70616G-page 209

11.1.1

OPEN-DRAIN CONFIGURATION

In addition to the PORT, LAT and TRIS registers for
data control, some port pins can also be individually
configured for either digital or open-drain output. This
is controlled by the Open-Drain Control register,
ODCx, associated with each port. Setting any of the
bits configures the corresponding pin to act as an
open-drain output. 
The open-drain feature allows the generation of
outputs higher than V

DD

 (e.g., 5V on a 5V tolerant pin)

by using external pull-up resistors. The maximum
open-drain voltage allowed is the same as the
maximum V

IH

 specification for that pin. 

See the “

” section for the available pins

and their functionality.

The ANSELx register controls the operation of the
analog port pins. The port pins that are to function as
analog inputs or outputs must have their corresponding
ANSELx and TRISx bits set. In order to use port pins for
I/O functionality with digital modules, such as Timers,
UARTs, etc., the corresponding ANSELx bit must be
cleared.
The ANSELx register has a default value of 0xFFFF;
therefore, all pins that share analog functions are
analog (not digital) by default. Refer to the Pinout I/O
Descriptions (

) for the complete list of analog pins.

If the TRISx bit is cleared (output) while the ANSELx bit
is set, the digital output level (V

OH

 or V

OL

) is converted

by an analog peripheral, such as the ADC module or
Comparator module.
When the PORT register is read, all pins configured as
analog input channels are read as cleared (a low level).
Pins configured as digital inputs do not convert an
analog input. Analog levels on any pin defined as a
digital input (including the pins defined as Analog in

 in 

) can

cause the input buffer to consume current that
exceeds the device specifications.

11.2.1

I/O PORT WRITE/READ TIMING

One instruction cycle is required between a port
direction change or port write operation and a read
operation of the same port. Typically this instruction
would be an NOP, as shown in 

.

The input change notification function of the I/O ports
allows the dsPIC33EPXXX(GP/MC/MU)806/810/814
and PIC24EPXXX(GP/GU)810/814 devices to
generate interrupt requests to the processor in
response to a Change-of-State (COS) on selected input
pins. This feature can detect input Change-of-States
even in Sleep mode, when the clocks are disabled.
Every I/O port pin can be selected (enabled) for
generating an interrupt request on a Change-of-State.
Three control registers are associated with the CN
functionality of each I/O port. The CNENx registers
contain the CN interrupt enable control bits for each of
the input pins. Setting any of these bits enables a CN
interrupt for the corresponding pins.
Each I/O pin also has a weak pull-up and a weak
pull-down connected to it. The pull-ups act as a
current source or sink source connected to the pin,
and eliminate the need for external resistors when
push-button or keypad devices are connected. The
pull-ups and pull-downs are enabled separately using
the CNPUx and the CNPDx registers, which contain
the control bits for each of the pins. Setting any of
the control bits enables the weak pull-ups and/or
pull-downs for the corresponding pins.

Pull-ups and pull-downs on change notifi-
cation pins should always be disabled
when the port pin is configured as a digital
output.

MOV

0xFF00, W0

; Configure PORTB<15:8>
; as inputs

MOV

W0, TRISB

; and PORTB<7:0> 
; as outputs

NOP

; Delay 1 cycle

BTSS

PORTB, #13

; Next Instruction