View source for 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.

[https://www.digikey.com/product-detail/en/maxlinear-inc/XR21B1420IL28-0A-EVB/1016-2062-ND/5080589 MaxLinear XR21B1420IL28-0A-EVB | DigiKey]

[https://www.mouser.com/ProductDetail/MaxLinear/XR21B1420IL28-0A-EVB?qs=C8E66ftkQtzee90NEaObRg%3D%3D MaxLinear XR21B1420IL28-0A-EVB | Mouser]

== Wiring Diagram ==

{| class="wikitable"
! DB9 Pin
! RS-232
! RS-422
! RS-485
|-
| 1
| DCD
| TX-
| Data-
|-
| 2
| RXD
| TX+
| Data+
|-
| 3
| TXD
| RX+
| 
|-
| 4
| DTR
| RX-
| 
|-
| 5
| colspan="3" | (GND)
|-
| 6
| DSR
| 
| 
|-
| 7
| RTS
| 
| 
|-
| 8
| CTS
| 
| 
|-
| 9
| RI
| 
| 
|}

* [https://www.maxlinear.com/ds/sp339e.pdf#page=5 Page 5] of the SP339E datasheet shows the DE9 pinout

== Jumpers ==

{| class="wikitable"
! Name
! Default
! Function
|-
| J2
| 1 &amp; 2 (down)
| 1 &amp; 2 (down): VCC_OUT to VCC_TRANS<br/>2 &amp; 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 &amp; 2 (right)
| 1 &amp; 2 (right): VCC_USB to VCC_UART<br/>2 &amp; 3 (left): VCC_3V3 to VCC_UART
|-
| J11
| (not present)
| 1 &amp; 2 (left): VCC_OUT to VIO<br/>2 &amp; 3 (right): VIO_EXTERNAL to VIO
|-
| J12
| 1 &amp; 2 (down)
| 1 &amp; 2 (down): GPIO7/!RI/!RWK to SW1 button<br/> 2 &amp; 3 (up): GPIO7/!RI/!RWK to !RI_TRANS
|-
| J13
| 2 &amp; 3 (left)
| 1 &amp; 2 (right): VIO to VCC<br/>2 &amp; 3 (left): VCC_OUT to VCC
|-
| J15
| 2 &amp; 3 (up)
| 1 &amp; 2 (down):<br/>2 &amp; 3 (up)
|-
| J17
| 2 &amp; 3 (up)
| 1 &amp; 2 (down): TXT_MODE1 to TXT<br/>2 &amp; 3 (up): pullup/D1 LED to TXT
|-
| J18
| ???
| TODO
|-
| J19
| (not present)
| 1 &amp; 2: connects the regulated 3.3V from the SP6260 to the VCC pin of the XR21B1420
|-
| J20
| 1 &amp; 2
| 1 &amp; 2: GPIO9/!DSR to !DSR (transceiver) NOTE: manual claims GPIO2? schematic says GPIO9...
|-
| J21
| 
| 1 &amp; 2 (down): XEN to J37 pin 3 <br/>2 &amp; 3 (up): !RTS_XEN to J37 pin 3
|-
| J23
| 
| ...<br/>3 &amp; 4: VCC_USB to !RESET</br>...
|-
| J24
| 
| (various debug signals)
|-
| J37
| 
| ...<br/>3 &amp; 4 (2nd from left): XEN or !RTS_XEN to DIR1</br>...
|}

== Software ==

To get full functionality under Linux, you must install the <code>xr_usb_serial_common</code> kernel module. The drivers are available here:

[https://www.maxlinear.com/support/design-tools/software-drivers Software Drivers - MaxLinear]

In the "USB UART" section in their downloads table, pick the latest version for Linux. Here is a direct link to version 1D for "Linux 3.6.x and newer":

[https://assets.maxlinear.com/web/documents/xr_usb_serial_common_lnx-3.6-and-newer-pak_v1d.zip xr_usb_serial_common_lnx-3.6-and-newer-pak_v1d.zip]

<del>[https://www.maxlinear.com/content/document.ashx?id=21651 xr_usb_serial_common_lnx-3.6-and-newer-pak.zip]</del> (1C was superseded by 1D)

If successfully installed, when the USB device (<code>04e2:1420 Exar Corp.</code>) is connected it the device node <code>/dev/ttyXRUSB0</code> should show up.

== Bill of Materials ==

{| class="wikitable"
! Name
! Part
|-
| U2
| [https://www.digikey.com/product-detail/en/maxlinear-inc/SP339ECR1-L/1016-1703-ND/2770686 MaxLinear SP339ECR1-L]
|-
| U3
| [https://www.digikey.com/product-detail/en/maxlinear-inc/XR21B1420IL28-F/1016-2063-ND/5080590 MaxLinear XR21B1420IL28-F]
|}

== Online Resources ==

[https://www.maxlinear.com/document/21623/xr21b1420il28-0a-evb_usersmanual_1a_080514.pdf Exar XR21B1420IL28-0A-EVB Evaluation Board User’s Manual Rev 1A]

[https://www.maxlinear.com/document/21620/xr21b1420_1421_sch_rev10_9182014.pdf Exar XR21B1420/21 Evaluation Board Schematic Rev 1.0]

[https://www.maxlinear.com/ds/xr21b1420.pdf MaxLinear XR21B1420 Datasheet]

[https://www.maxlinear.com/ds/sp339e.pdf MaxLinear SP339E Datasheet]

[https://www.maxlinear.com/product/interface/uarts/usb-uarts/xr21b1420 XR21B1420 - MaxLinear]

<del>[http://www.bdtic.com/download/exar/21623 Exar XR21B1420IL28-0A-EVB Evaluation Board User’s Manual Rev 1A]</del>

<del>[http://www.bdtic.com/download/exar/21620 Exar XR21B1420/21 Evaluation Board Schematic Rev 1.0]</del>

<del>[http://www.exar.com/common/content/document.ashx?id=21620 Exar XR21B1420/21 Evaluation Board Schematic Rev 1.0]</del>

[https://www.avrfreaks.net/comment/1573101#comment-1573101 running Due at 1Mbaud and 2.5M baud <nowiki>[SOLVED]</nowiki> | AVR Freaks]