© 2014 Exar Corporation
XR21B1424IV64-0A-EVB
5 / 6
exar.com/XR21B1424
Rev 1A
GPIO9/RXT
When shipped from the factory, the GPIO9/RXT pin is floating. This pin can be used to control the MODE2 pin of the
SP339. If using this pin to control the MODE2 pin of the SP339, install jumpers for the appropriate channels listed in
Table 8. The software driver/application will need to control the state of this pin.
SP338/SP339 Mode Selection
When shipped from the factory, the SP338/SP339 transceivers are configured in the RS-232 mode. Table 9 shows the RS-
232 settings for the SP339.
There are 2 sets of headers for each UART channel for configuring the mode of the SP339 transceiver. For example, chan-
nel A uses J5 and J4. For the RS-232 mode, there is a jumper from J5 pin 2 to J4 pin 1. Refer to the table in the schematic
or the SP339 datasheet for the different configurations.
By default, the ENABLE of the SP339 transceiver is controlled by the USB_STAT2 pin of the XR21B1424.
Half-duplex, Full-Duplex and Mixed Duplex RS-485/422 modes
In the RS-485 half-duplex, full-duplex and mixed duplex modes, the DIR1 pin of the SP338/SP339 enables or disables the
RS-485/422 line drivers. The DIR1 pin can be controlled by the XR21B1424 using the GPIO7/RS485 or GPIO5/RTS#/
RS485 output pins. The GPIO7/RS485 or GPIO5/RTS#/RS485 pin can be selected via J21. Refer to the datasheet for
details for selecting and enabling the Automatic Transceiver Enable feature for the GPIO7/RS485 or GPIO5/RTS#/RS485
pins.
Software and Technical Support
Software drivers and test applications should be included in the CD that accompanies the evaluation board. Send any ques-
tions that you may have to [email protected].
Table 8: Default Jumper Setting for GPIO9/RXT
Jumper Setting
Description
J5 - 5 & 6
Not installed. GPIOA9/RXTA is not connected to the MODE2 pin of the SP339.
J10 - 5 & 6
Not installed. GPIOB9/RXTB is not connected to the MODE2 pin of the SP339.
J11 - 5 & 6
Not installed. GPIOC9/RXTC is not connected to the MODE2 pin of the SP339.
J20 - 5 & 6
Not installed. GPIOD9/RXTD is not connected to the MODE2 pin of the SP339.
Table 9: SP339 RS-232 Mode Pin Configurations
Mode
Configuration
MODE0
1
MODE1
0
MODE2
0
