Microchip Technology MA330019-2 Data Sheet
dsPIC33FJ32GP302/304, dsPIC33FJ64GPX02/X04, AND dsPIC33FJ128GPX02/X04
DS70292G-page 222
© 2007-2012 Microchip Technology Inc.
18.1
UART Helpful Tips
1.
In multi-node direct-connect UART networks,
UART receive inputs react to the
complementary 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 ini-
tialized 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
UART receive inputs react to the
complementary 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 ini-
tialized 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, resulting in the
first character being invalid. This is to be
expected.
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, resulting 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 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
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.
18.2.1
KEY RESOURCES
• Section 17. “UART” (DS70188)
• Code Samples
• Application Notes
• Software Libraries
• Webinars
• All related dsPIC33F/PIC24H Family Reference
• Code Samples
• Application Notes
• Software Libraries
• Webinars
• All related dsPIC33F/PIC24H Family Reference
Manuals Sections
• Development Tools
Note:
In the event you are not able to access the
product page using the link above, enter
this URL in your browser:
product page using the link above, enter
this URL in your browser: