Microchip Technology MA330027 Data Sheet

DS70616G-page 354

 2009-2012 Microchip Technology Inc.

1.

In multi-node direct-connect UARTx networks,
UARTx receive inputs react to the complemen-
tary logic level defined by the URXINV bit
(UxMODE<4>), which defines the Idle state, the
default of which is logic high (i.e., URXINV = 0).
Because remote devices do not initialize at the
same time, it is likely that one of the devices,
because the RX line is floating, will trigger a
Start bit detection and will cause the first byte
received, after the device has been initialized, to
be invalid. To avoid this situation, the user
should use a pull-up or pull-down resistor on the
RX pin depending on the value of the URXINV
bit.
a) If URXINV = 0, use a pull-up resistor on the

RX pin.

b) If URXINV = 1, use a pull-down resistor on

the RX pin. 

2.

The first character received on a wake-up from
Sleep mode, caused by activity on the UxRX pin
of the UARTx module, will be invalid. In Sleep
mode, peripheral clocks are disabled. By the
time the oscillator system has restarted and
stabilized from Sleep mode, the baud rate bit
sampling clock, relative to the incoming UxRX
bit timing, is no longer synchronized resulting in
the first character being invalid. This is to be
expected.

Many useful resources related to the UARTx are
provided on the main product page of the Microchip
web site for the devices listed in this data sheet. This
product page, which can be accessed using this 

contains the latest updates and additional information.

20.2.1

KEY RESOURCES

• Section 17. “UART” (DS70582) in the 

• Code Samples
• Application Notes
• Software Libraries
• Webinars
• All related “dsPIC33E/PIC24E Family Reference 

Manual” Sections

• Development Tools

In the event you are not able to access the
product page using the link above, enter
this URL in your browser: