Erich Styger provided an excellent description of how to connect the FTDI-based Embest UART8000-U USB-to-TTL cable to the J18 interface on the RIoTboard in order to create a system console on a Windows host in the following post
http://mcuoneclipse.com/2014/07/21/terminal-connection-to-the-riot-board/
This post will describe how to connect a Prolific-based JBtek/Adafruit USB-to-TTL cable to the RIoTboard J18 interface in order to create a system console on a Windows host in conjunction with Tera Term (a Windows communication program). Important differences between Styger's setup and the JBtek setup as well as some additional points to bear in mind will be also be discussed.
(***IMPORTANT DISCLOSURE***: While I have used and tested two of the JBtek cables with the RIoTboard, I do not own nor have I tested the Adafruit 954 cable discussed below. Hopefully, someone in the community who has both the Adafruit 954 (second revision) and a RIoTboard can confirm that same procedure described below works for that particular cable as well.)
The Jbtek/Adafruit 954 USB-to-TTL Serial Cable
The cable I used to create a system terminal is a “JBtek
WINDOWS 8 Supported Debug Cable for Raspberry Pi USB Programming USB to TTL Serial Cable“ available from Amazon.com:
http://www.amazon.com/JBtek%C2%AE-WINDOWS-Supported-Raspberry-Programming/dp/B00QT7LQ88
This cable uses a Prolific PL2303TA device according to Prolific's CheckChip utility on one of my Windows 7 machines. Unfortunately, it ships with zero documentation or drivers.
While I have been unable to find an unequivocal statement from either JBtek or Adafruit Industries that the JBtek cable I purchased is identical to the Adafruit 954 product, there is a great deal of evidence to suggest that they are almost, if not completely, identical:
https://www.adafruit.com/product/954
http://www.amazon.com/ADAFRUIT-INDUSTRIES-954-USB-TO-TTL-RASPBERRY/dp/B00DJUHGHI
The Adafruit page for the 954 cable indicates the following:
Revision History
Prior to July 1 2014 this cable would come with a PL2303HX chipset and a black USB body. After July 1, 2014 we changed to a violet body and the PL2303TA chipset. The new 'TA cables are Win8 compatible, and are more reliable especially when dealing with random USB-disconnects.
Newark/element14 sell the Adafruit 954 (in some locales), but the picture on the Newark/element14 site seems to show the earlier revision, so it isn't obvious whether they are in fact selling the most recent revision of the Adafruit 954:
http://www.newark.com/adafruit-industries/954/usb-to-ttl-serial-cable-raspberry/dp/44W3509
Windows Drivers for the JBtek Cable
I used the Version 1.12.0 PL2303 driver (PL2303_Prolific_DriverInstaller_v1_12_0.zip) available here to install the needed Prolific driver on both Windows 7 and Windows 8.1 machines prior to connecting the JBtek cable:
http://prolificusa.com/pl-2303hx-drivers/
This driver package also contains the CheckChip utility mentioned above if you are uncertain or concerned about which exact Prolific chip your cable is using. In order to use the CheckChip utility, you have to know which COM port the cable is using, and that means the device has to be successfully installed prior to using the utility.
Connecting the Cable to the RIoTboard
In order to physically connect the JBtek (or Adafruit) serial cable to the RIoTboard J18 interface, use the following connections (with no power applied to the RIoTboard):
JBtek White wire (RXD) to J18 Pin 1 (UART2_TXD) (farthest pin from corner of board)
JBtek Green wire (TXD) to J18 Pin 2 (UART2_RXD) (middle pin)
JBtek Black wire (GND) to J18 Pin 3 (GND) (pin closest to corner of board)
JBtek Red wire (5V) is unconnected
Here is a photo of the J18 interface after the JBtek cable has been connected (references to Pin numbers in the photo correspond to the J18.pin-out, not the JBtek cable):
If you compare the photo above with that provided by Erich Styger for the Embest UART8000-U cable connection in his post(mentioned and linked above one very important point stands out there is no common color coding scheme for these serial cables In other words if you try to connect the JBtek(or Adafruit cable to the RIoTboard by matching the wire colors in Styger's photo you will mis-connect the cable Guaranteed Also remember this fact if you are trying to connect some other cable not discussed in this post because it may well have a different pin-out/color scheme compared to any discussed here For example some serial cables have CTS/RTS lines as well
Another point that is probably worth mentioning has to do with the unconnected JBtek red wire (+5 Volts). If you look carefully at the photo above, you can see that the internal metal structure of the box-shaped connector on the end of the red wire is not entirely shielded by the insulating plastic (look at the edge of the Pin 3 bubble where it overlaps the connector). For the connectors attached directly to the RIoTboard J18 interface, this is not likely to cause problems, but the exposed metal on the loose JBtek red wire connector might come into contact with the grounded shells on the RIoTboard Ethernet or USB connectors for example. Therefore, it is a good idea to completely cover the connector on the JBtek red wire with some sort of insulation to prevent inadvertent contact with anything on the RIoTboard when the USB end of the cable has been mated to a USB port.
Configuring Tera Term
In order to display output from the J18 Serial Debug port using Tera Term (Version 4.89) on a Windows computer, do the following (assuming a fresh install):
1. Start Tera Term
2. Click the Serial radio button and select the COM port labeled “Prolific USB-to-Serial Comm Port”
3. Click the OK button
4. Click the Setup tab in the Tera Term VT window and select Serial Port
5. Change the Baud Rate to 115200 and click the OK button (Other parameters should be as follows by default: Data: 8 bit; Parity: none; Stop: 1 bit; Flow control: none)
6. Click the Setup tab in the Tera Term VT window and select General...
7. In the Tera Term General Setup dialog box, change the Language from UTF-8 to English (if you fail to do this, you will see terminal output, but it will be garbled)
8. Apply power to the RIoTboard and output should now appear in the Tera Term VT window