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SP338/SP339/XR34350 EVALUATION BOARD USER’S MANUAL
REV. 2.0.1
3.0 EVALUATING THE SP338/339/XR34350 TRANSCEIVER ONLY
When evaluating just the SP338/339/XR34350, an external power supply can be used or power from a USB
port can be used.
3.1
External Power Supply
An ex3.3V or +5V power supply can be applied at TP2. The USB cable should not be plugged into a
USB port and J17 should not be installed. Of course, there should be a common ground between the external
power supply and the SP338/339/XR34350.
3.2
USB Powered
If using power from a USB port, select the supply voltage at J4. A jumper across J4 pins 1 & 2 selects the 5V
from the USB connector. A jumper across J4 pins 2 & 3 selects the regulated 3.3V output from the SP6260. A
jumper across J17 pins 1& 2 will also need to be installed for power to be supplied to the SP338/339/XR34350.
A jumper should also be installed across J2 pins 1 & 2 (or 3 & 4) to ensure that there’s a common ground
between the USB supplied voltage and the SP338/339/XR34350.
4.0 EVALUATING THE SP338/339/XR34350 WITH THE XR21B1411
The XR21B1411 can be used to pass data through the SP338/339/XR34350. An external power supply can be
used or can be powered directly from the USB bus, as described above. A jumper should also be installed
across J2 pins 1 & 2 (or 3 & 4) to ensure that there’s a common ground between the XR21B1411 and SP338/
339/XR34350. To enable the connection between the XR21B1411 and the SP338/339/XR34350, place the
switches at SW3 to the ON position. In addition, if the DB9 connector is used, place the switches at SW4 in the
ON position. Windows, Linux and Mac drivers for the XR21B1411 can be downloaded from Exar’s website.
For Windows, a sample USB UART test GUI is also available for download.
4.1
Loopback Mode or RS-232 Mode
The XR21B1411 can transmit and receive data through the SP338/339/XR34350 if the switches at SW3 and
SW4 are in the ON position. For RS-232 mode, an external null modem cable or connection is required to
transmit and receive data.
4.2
Half-duplex, Full-Duplex and Mixed Duplex RS-485/422 modes
Some additional jumpers are required if there is a requirement to control the DIR1 and/or DIR2 pins from the
software driver or application. There should not be any jumpers installed on J23 pins 3 & 4 and pins 5 & 6.
4.2.1
Controlling DIR1 pin using RTS# output pin of XR21B1411
The DIR1 pin can be controlled from the XR21B1411 using the RTS# output pin. To enable the connection
between the RTS# pin of the XR21B1411 and the DIR1 pin, install a jumper across J20 pins 1 & 2. If using the
Windows 2000/XP/Vista/7/8 driver from Exar’s website, the "RS-485" mode can be enabled from the properties
page and will be enabled if used with any standard terminal application. Alternatively, the "RS-485" mode can
be enabled using the sample USB UART test GUI from Exar’s website. When transmitting data, the RTS# pin
will be high. While not transmitting data (receiving or idle), the RTS# pin will be low. This feature will work for
both the half-duplex RS-485 modes and full-duplex RS-485/422 modes.
4.2.2
Controlling DIR2 pin using DTR# output pin of XR21B1411
The DIR2 pin can be controlled from the XR21B1411 using the DTR# output pin. To enable the connection
between the DTR# pin of the XR21B1411 and the DIR2 pin, install a jumper across J21 pins 1 & 2. There’s no
automatic direction control feature with the DTR# pin. However, the DTR# pin can be controlled manually from
the software. The DTR# can use the standard "set DTR" and "clear DTR" APIs in Windows or Linux to set/
clear the DTR# pin. The DTR# pin can also be set/cleared by writing directly to the GPIO_SET and
GPIO_CLEAR registers using the sample USB UART test GUI from Exar’s website.
