MaxLinear XR21B1420IL28-0A-EVB USB to RS-232/422/485 Evaluation Board
Overview
USB to serial evaluation board. Supports RS-232, RS-422, and RS-485. Made by MaxLinear, formerly Exar. Supposedly supports higher than usual baudrates, up to 12Mbaud.
MaxLinear XR21B1420IL28-0A-EVB | DigiKey
MaxLinear XR21B1420IL28-0A-EVB | Mouser
Wiring Diagram
| DB9 Pin | RS-232 | RS-422 | RS-485 |
|---|---|---|---|
| 1 | DCD | TX- | Data- |
| 2 | RXD | TX+ | Data+ |
| 3 | TXD | RX+ | |
| 4 | DTR | RX- | |
| 5 | (GND) | ||
| 6 | DSR | ||
| 7 | RTS | ||
| 8 | CTS | ||
| 9 | RI | ||
- Page 5 of the SP339E datasheet shows the DE9 pinout
Jumpers
| Name | Default | Function |
|---|---|---|
| J2 | 1 & 2 (down) | 1 & 2 (down): VCC_OUT to VCC_TRANS 2 & 3 (up): VCC_USB to VCC_TRANS |
| J3 | pins map to DE9 connector, except pin 5 (GND) is skipped | |
| J4 | 47k pull-ups to VCC_TRANS for jumpering to J18 | |
| J10 | 1 & 2 (right) | 1 & 2 (right): VCC_USB to VCC_UART 2 & 3 (left): VCC_3V3 to VCC_UART |
| J11 | (not present) | 1 & 2 (left): VCC_OUT to VIO 2 & 3 (right): VIO_EXTERNAL to VIO |
| J12 | 1 & 2 (down) | 1 & 2 (down): GPIO7/!RI/!RWK to SW1 button 2 & 3 (up): GPIO7/!RI/!RWK to !RI_TRANS |
| J13 | 2 & 3 (left) | 1 & 2 (right): VIO to VCC 2 & 3 (left): VCC_OUT to VCC |
| J15 | 2 & 3 (up) | 1 & 2 (down): 2 & 3 (up) |
| J17 | 2 & 3 (up) | 1 & 2 (down): TXT_MODE1 to TXT 2 & 3 (up): pullup/D1 LED to TXT |
| J18 | ??? | TODO |
| J19 | (not present) | 1 & 2: connects the regulated 3.3V from the SP6260 to the VCC pin of the XR21B1420 |
| J20 | 1 & 2 | 1 & 2: GPIO9/!DSR to !DSR (transceiver) NOTE: manual claims GPIO2? schematic says GPIO9... |
| J21 | 1 & 2 (down): XEN to J37 pin 3 2 & 3 (up): !RTS_XEN to J37 pin 3 | |
| J23 | ... 3 & 4: VCC_USB to !RESET ... | |
| J24 | (various debug signals) | |
| J37 | ... 3 & 4 (2nd from left): XEN or !RTS_XEN to DIR1 ... |
Software
To get full functionality under Linux, you must install the xr_usb_serial_common kernel module. The drivers are available here:
In the "USB UART" section in their downloads table, pick the latest version for Linux. Here is a direct link to version 1C for "Linux 3.6.x and newer":
xr_usb_serial_common_lnx-3.6-and-newer-pak.zip
If successfully installed, when the USB device (04e2:1420 Exar Corp.) is connected it the device node /dev/ttyXRUSB0 should show up.
Bill of Materials
| Name | Part |
|---|---|
| U2 | MaxLinear SP339ECR1-L |
| U3 | MaxLinear XR21B1420IL28-F |
Online Resources
Exar XR21B1420IL28-0A-EVB Evaluation Board User’s Manual Rev 1A
Exar XR21B1420/21 Evaluation Board Schematic Rev 1.0
Exar XR21B1420IL28-0A-EVB Evaluation Board User’s Manual Rev 1A
Exar XR21B1420/21 Evaluation Board Schematic Rev 1.0