Datasheet

dsPIC33FJ06GS001/101A/102A/202A and dsPIC33FJ09GS302
DS75018C-page 220  2011-2012 Microchip Technology Inc.
18.1 UART Helpful Tips
1. In multinode, direct-connect UART networks,
UART receive inputs react to the complemen-
tary logic level defined by the URXINV bit
(U1MODE<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 UART 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. This results in the first
character being invalid; this is to be expected.
18.2 UART Resources
Many useful resources related to UART are provided
on the Microchip web site (www.microchip.com).
18.2.1 KEY RESOURCES
• Section 17. “UART” (DS70188) in the
“dsPIC33F/PIC24H Family Reference Manual”
• Code Samples
• Application Notes
• Software Libraries
• Webinars
• All related “dsPIC33F/PIC24H Family Reference
Manual” Sections
• Development Tools